title
React Component Lifecycle - Hooks / Methods Explained

description
React components have several lifecycle methods that you can override to run your code at a particular time in the process. In this video, we will explore all the React Component Lifecycle methods. Tutorial from Nick Karnik. Check out his YouTube channel: https://www.youtube.com/channel/UClCm-WAOgN6XLwCpefSVezg Nick on Twitter: https://twitter.com/theoutlander -- Learn to code for free and get a developer job: https://www.freecodecamp.org Read hundreds of articles on programming: https://medium.freecodecamp.org

detail
{'title': 'React Component Lifecycle - Hooks / Methods Explained', 'heatmap': [{'end': 409.138, 'start': 383.185, 'weight': 0.733}, {'end': 1079.873, 'start': 1045.7, 'weight': 0.837}], 'summary': 'Covers react component lifecycle, methods for mounting, updating, error boundaries, and unmounting, prop passing, component updates, efficient state management, and error handling, emphasizing the importance of using these methods correctly to optimize performance.', 'chapters': [{'end': 158.902, 'segs': [{'end': 82.741, 'src': 'embed', 'start': 25.785, 'weight': 0, 'content': [{'end': 32.71, 'text': 'Components have several lifecycle methods that you can override to run your code at a particular time in the process.', 'start': 25.785, 'duration': 6.925}, {'end': 41.117, 'text': 'These methods are categorized into four groups, mounting, updating, error boundaries, and unmounting.', 'start': 33.551, 'duration': 7.566}, {'end': 48.182, 'text': 'In this example, we will build a counter component and utilize all the lifecycle methods.', 'start': 42.237, 'duration': 5.945}, {'end': 51.777, 'text': "Let's get started with creating a constructor.", 'start': 49.076, 'duration': 2.701}, {'end': 63.102, 'text': 'A constructor takes props as its object, and we need to call the base class or the parent class method via super and pass in props.', 'start': 51.797, 'duration': 11.305}, {'end': 67.244, 'text': 'What this does is it sets this dot props to props.', 'start': 63.683, 'duration': 3.561}, {'end': 69.265, 'text': "So it's available throughout our class.", 'start': 67.744, 'duration': 1.521}, {'end': 73.407, 'text': 'Constructor is also the only place where we can set state.', 'start': 70.426, 'duration': 2.981}, {'end': 77.339, 'text': "So let's go ahead and set a counter.", 'start': 74.738, 'duration': 2.601}, {'end': 79.94, 'text': "And let's use that in the render method.", 'start': 78.399, 'duration': 1.541}, {'end': 82.741, 'text': 'All right.', 'start': 82.461, 'duration': 0.28}], 'summary': 'Lifecycle methods in a counter component, including constructor and render, are demonstrated.', 'duration': 56.956, 'max_score': 25.785, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c25785.jpg'}], 'start': 1.4, 'title': 'React component lifecycle', 'summary': 'Covers react component lifecycle, including the methods for mounting, updating, error boundaries, and unmounting, and building a counter component to utilize all the lifecycle methods.', 'chapters': [{'end': 158.902, 'start': 1.4, 'title': 'React component lifecycle', 'summary': 'Covers react component lifecycle, including the methods for mounting, updating, error boundaries, and unmounting, and building a counter component to utilize all the lifecycle methods.', 'duration': 157.502, 'highlights': ['Components have several lifecycle methods categorized into mounting, updating, error boundaries, and unmounting The chapter explains that components have several lifecycle methods that are categorized into four groups: mounting, updating, error boundaries, and unmounting.', 'Building a counter component to utilize all the lifecycle methods The chapter demonstrates building a counter component to utilize all the lifecycle methods, showcasing practical application of the discussed concepts.', 'Explaining the constructor as the only place to set state and the utilization of super to call the parent class method The chapter explains that the constructor is the only place to set state and utilizes super to call the parent class method, providing insight into the foundational aspects of React component setup.']}], 'duration': 157.502, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c1400.jpg', 'highlights': ['Building a counter component to utilize all the lifecycle methods', 'Components have several lifecycle methods categorized into mounting, updating, error boundaries, and unmounting', 'Explaining the constructor as the only place to set state and the utilization of super to call the parent class method']}, {'end': 487.544, 'segs': [{'end': 254.974, 'src': 'embed', 'start': 159.122, 'weight': 0, 'content': [{'end': 166.887, 'text': "Now, when we click this, we're going to see the counter reflect the change and notice that all that's doing right now is calling the render method.", 'start': 159.122, 'duration': 7.765}, {'end': 170.07, 'text': "So let's introduce a few lifecycle methods.", 'start': 167.888, 'duration': 2.182}, {'end': 174.492, 'text': 'The first one is componentDidMount.', 'start': 170.73, 'duration': 3.762}, {'end': 178.415, 'text': 'This is called right after render.', 'start': 176.614, 'duration': 1.801}, {'end': 188.297, 'text': "And when I save this, we'll see things re-render.", 'start': 185.936, 'duration': 2.361}, {'end': 194.52, 'text': 'And what I want to do is also add markers at the end of some of these render life cycles.', 'start': 188.657, 'duration': 5.863}, {'end': 200.962, 'text': "So we're just going to add a dashed line so we know that this is a single render call.", 'start': 195.72, 'duration': 5.242}, {'end': 204.944, 'text': 'And if we were to do increment, there is another render call.', 'start': 201.963, 'duration': 2.981}, {'end': 213.648, 'text': 'But it does not call component and mount because that is only triggered when the component is constructed and essentially gets added into the DOM.', 'start': 205.344, 'duration': 8.304}, {'end': 219.7, 'text': "However, there's another method called componentDidUpdate.", 'start': 214.898, 'duration': 4.802}, {'end': 224.282, 'text': 'And this method actually takes a few parameters.', 'start': 221.021, 'duration': 3.261}, {'end': 231.025, 'text': "There's a reference to previous props, the previous date, and snapshot.", 'start': 225.043, 'duration': 5.982}, {'end': 240.81, 'text': "Let's trigger componentDidUpdate and we'll add a log statement here.", 'start': 234.907, 'duration': 5.903}, {'end': 251.351, 'text': 'All right, so notice that component update is not called here.', 'start': 248.089, 'duration': 3.262}, {'end': 254.974, 'text': "Once we click increment, we'll see component update.", 'start': 251.671, 'duration': 3.303}], 'summary': 'Introducing lifecycle methods: componentdidmount, componentdidupdate, and render; with markers and re-renders.', 'duration': 95.852, 'max_score': 159.122, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c159122.jpg'}, {'end': 432.616, 'src': 'heatmap', 'start': 383.185, 'weight': 4, 'content': [{'end': 386.507, 'text': "And if it's not set to mount, we'll remove it from the DOM.", 'start': 383.185, 'duration': 3.322}, {'end': 388.789, 'text': 'All right, so there you go.', 'start': 387.748, 'duration': 1.041}, {'end': 393.853, 'text': 'So now this should actually remove the counter.', 'start': 389.469, 'duration': 4.384}, {'end': 398.592, 'text': "Let's add another lifecycle method in counter.", 'start': 395.47, 'duration': 3.122}, {'end': 402.974, 'text': "This time it's called component will unmount.", 'start': 399.052, 'duration': 3.922}, {'end': 409.138, 'text': 'As the name suggests, this method is called when a component is being taken out of the DOM.', 'start': 404.235, 'duration': 4.903}, {'end': 414.901, 'text': "Let's add another marker there.", 'start': 413.62, 'duration': 1.281}, {'end': 416.502, 'text': 'There you go.', 'start': 416.002, 'duration': 0.5}, {'end': 418.063, 'text': 'So now component did mount.', 'start': 416.982, 'duration': 1.081}, {'end': 421.905, 'text': "If I click on mount counter, you'll see component will unmount was triggered.", 'start': 418.143, 'duration': 3.762}, {'end': 424.233, 'text': 'There you go.', 'start': 423.112, 'duration': 1.121}, {'end': 429.555, 'text': 'On mount, the constructor is triggered because the counter component is recreated.', 'start': 424.433, 'duration': 5.122}, {'end': 432.616, 'text': 'These are the most commonly used lifecycle methods.', 'start': 429.915, 'duration': 2.701}], 'summary': 'Demonstrating the usage of lifecycle methods in component, including componentdidmount and componentwillunmount.', 'duration': 28.381, 'max_score': 383.185, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c383185.jpg'}], 'start': 159.122, 'title': 'React component lifecycle methods', 'summary': 'Introduces lifecycle methods in react components, including componentdidmount, and highlights the rendering behavior triggered by these methods. it covers the overview of commonly used react lifecycle methods such as componentdidupdate, componentdidmount, and componentwillunmount, as well as infrequently used methods like shouldcomponentupdate, emphasizing the importance of using these methods correctly to optimize performance.', 'chapters': [{'end': 213.648, 'start': 159.122, 'title': 'React component lifecycle', 'summary': 'Introduces lifecycle methods in react components, including componentdidmount, and highlights the rendering behavior triggered by these methods.', 'duration': 54.526, 'highlights': ['The chapter introduces componentDidMount, a lifecycle method in React components, called after the render, triggering re-rendering.', 'The rendering behavior is explained with the addition of markers to denote single render calls and the absence of componentDidMount triggering on incremental render.']}, {'end': 487.544, 'start': 214.898, 'title': 'React lifecycle methods overview', 'summary': 'Covers the overview of commonly used react lifecycle methods such as componentdidupdate, componentdidmount, and componentwillunmount, as well as infrequently used methods like shouldcomponentupdate. it also emphasizes the importance of using these methods correctly to optimize performance.', 'duration': 272.646, 'highlights': ['The chapter covers commonly used React lifecycle methods such as componentDidUpdate, componentDidMount, and componentWillUnmount, as well as infrequently used methods like shouldComponentUpdate.', 'The componentDidUpdate method takes parameters including previous props, previous date, and snapshot, and is triggered when the component updates.', 'The componentWillUnmount method is called when a component is being taken out of the DOM, and shouldComponentUpdate is used to let React know if render should be triggered, potentially optimizing performance.']}], 'duration': 328.422, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c159122.jpg', 'highlights': ['The chapter introduces componentDidMount, a lifecycle method in React components, called after the render, triggering re-rendering.', 'The chapter covers commonly used React lifecycle methods such as componentDidUpdate, componentDidMount, and componentWillUnmount, as well as infrequently used methods like shouldComponentUpdate.', 'The rendering behavior is explained with the addition of markers to denote single render calls and the absence of componentDidMount triggering on incremental render.', 'The componentDidUpdate method takes parameters including previous props, previous date, and snapshot, and is triggered when the component updates.', 'The componentWillUnmount method is called when a component is being taken out of the DOM, and shouldComponentUpdate is used to let React know if render should be triggered, potentially optimizing performance.']}, {'end': 886.469, 'segs': [{'end': 584.81, 'src': 'embed', 'start': 488.605, 'weight': 0, 'content': [{'end': 494.908, 'text': "Let's add a prop in app.js that we're going to pass into counter, which we would want to ignore.", 'start': 488.605, 'duration': 6.303}, {'end': 498.651, 'text': "Okay, so let's call it ignore prop.", 'start': 494.929, 'duration': 3.722}, {'end': 502.526, 'text': "And whatever the value here is, let's say it's zero.", 'start': 500.402, 'duration': 2.124}, {'end': 512.385, 'text': "initially. I'm going to create another method here to pass and ignore prop by generating a value and assigning it to state.", 'start': 502.526, 'duration': 9.859}, {'end': 519.394, 'text': 'So ignore prop is just add the random.', 'start': 514.251, 'duration': 5.143}, {'end': 520.953, 'text': "We don't care what the value is.", 'start': 519.894, 'duration': 1.059}, {'end': 527.376, 'text': 'What we want to do next is pass that prop into the counter.', 'start': 521.634, 'duration': 5.742}, {'end': 533.558, 'text': "So we'll pass an ignore prop equals this.state.ignore prop.", 'start': 528.256, 'duration': 5.302}, {'end': 540.4, 'text': 'And so that should pass this through.', 'start': 535.298, 'duration': 5.102}, {'end': 548.262, 'text': 'But what we also need is a button to trigger the change.', 'start': 543.137, 'duration': 5.125}, {'end': 552.727, 'text': "So let's call this ignore prop.", 'start': 549.163, 'duration': 3.564}, {'end': 558.453, 'text': 'And then on click, we will call this dot ignore prop.', 'start': 554.409, 'duration': 4.044}, {'end': 561.33, 'text': 'Okay, there you go.', 'start': 560.569, 'duration': 0.761}, {'end': 567.536, 'text': "So now, when I click ignore prop, it's going to call render and component update,", 'start': 561.39, 'duration': 6.146}, {'end': 573.702, 'text': 'mainly because something changed on the parent and that was passed down to the component.', 'start': 567.536, 'duration': 6.166}, {'end': 578.847, 'text': "But in this case, let's say we don't care about ignore prop because we're not doing anything with it.", 'start': 574.583, 'duration': 4.264}, {'end': 580.189, 'text': "We're not rendering it to the UI.", 'start': 578.947, 'duration': 1.242}, {'end': 582.409, 'text': 'So we simply want to ignore it.', 'start': 580.929, 'duration': 1.48}, {'end': 584.81, 'text': "That's where this method comes into the picture.", 'start': 583.25, 'duration': 1.56}], 'summary': 'Adding and passing an ignore prop value of zero into the counter component, with a method to ignore it and trigger a change.', 'duration': 96.205, 'max_score': 488.605, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c488605.jpg'}, {'end': 760.047, 'src': 'embed', 'start': 696.105, 'weight': 1, 'content': [{'end': 698.026, 'text': 'Ignore prop has been passed in there.', 'start': 696.105, 'duration': 1.921}, {'end': 701.407, 'text': 'Oh, this should be ignore prop.', 'start': 698.806, 'duration': 2.601}, {'end': 704.308, 'text': "That's the issue.", 'start': 703.628, 'duration': 0.68}, {'end': 706.868, 'text': 'All right, there you go.', 'start': 706.167, 'duration': 0.701}, {'end': 714.956, 'text': 'The next thing to look into is a method called getDerivedStateFromProps.', 'start': 708.91, 'duration': 6.046}, {'end': 720.962, 'text': "This is a static method, and it's called before every other method.", 'start': 715.777, 'duration': 5.185}, {'end': 729.571, 'text': 'And this passes in props and state.', 'start': 726.628, 'duration': 2.943}, {'end': 740.782, 'text': 'And the purpose of this method is to give you a chance to copy any values from props that you may be interested in transferring over to state.', 'start': 730.999, 'duration': 9.783}, {'end': 751.885, 'text': 'And in our case, we could add another method here that allows us to pass in a random seed value.', 'start': 742.602, 'duration': 9.283}, {'end': 760.047, 'text': "So let's say we start out with our seed being some arbitrary value here.", 'start': 753.165, 'duration': 6.882}], 'summary': 'Discussing getderivedstatefromprops method for transferring values from props to state.', 'duration': 63.942, 'max_score': 696.105, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c696105.jpg'}], 'start': 488.605, 'title': 'React.js prop passing and component update', 'summary': 'Covers prop passing in react.js, including creating and ignoring prop values, and introduces the getderivedstatefromprops method for efficient component updates and state management.', 'chapters': [{'end': 561.33, 'start': 488.605, 'title': 'React.js prop passing', 'summary': "Discusses the process of passing and ignoring prop values in a react.js application, including creating and passing an 'ignore prop' with an initial value of zero, generating a random value for the 'ignore prop', and triggering the change using a button click event.", 'duration': 72.725, 'highlights': ["Creating an 'ignore prop' with an initial value of zero in app.js to be passed into the counter.", "Generating a random value for the 'ignore prop' and assigning it to state for passing into the counter.", "Triggering the change of the 'ignore prop' using a button with an onClick event."]}, {'end': 886.469, 'start': 561.39, 'title': 'React component update and getderivedstatefromprops method', 'summary': 'Discusses how to optimize rendering in a react component and introduces the getderivedstatefromprops method to copy values from props to state, allowing for efficient management of component updates and state changes.', 'duration': 325.079, 'highlights': ['Introducing method to optimize rendering and ignore unnecessary prop changes The chapter discusses a method to optimize rendering in a React component by ignoring unnecessary prop changes, reducing unnecessary renders and improving performance.', 'Explanation of getDerivedStateFromProps method and its purpose The getDerivedStateFromProps method is introduced, which allows copying values from props to state, providing efficient management of component updates and state changes.', 'Utilizing getDerivedStateFromProps method to transfer seed value from props to state The chapter demonstrates the use of getDerivedStateFromProps method to transfer a seed value from props to state, enabling efficient management of state changes and triggering render updates based on prop changes.']}], 'duration': 397.864, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c488605.jpg', 'highlights': ['Introducing method to optimize rendering and ignore unnecessary prop changes', 'Utilizing getDerivedStateFromProps method to transfer seed value from props to state', 'Explanation of getDerivedStateFromProps method and its purpose', "Triggering the change of the 'ignore prop' using a button with an onClick event", "Generating a random value for the 'ignore prop' and assigning it to state for passing into the counter", "Creating an 'ignore prop' with an initial value of zero in app.js to be passed into the counter"]}, {'end': 1298.261, 'segs': [{'end': 949.891, 'src': 'embed', 'start': 886.929, 'weight': 0, 'content': [{'end': 894.511, 'text': 'But the point here was to demonstrate this lifecycle method that allows us to copy props into state.', 'start': 886.929, 'duration': 7.582}, {'end': 901.492, 'text': "Notice that since this is a static method, we don't have access to the instance of the object.", 'start': 895.871, 'duration': 5.621}, {'end': 905.153, 'text': "There's one more or a couple more methods we need to talk about.", 'start': 902.252, 'duration': 2.901}, {'end': 909.453, 'text': 'So the next one is called getSnapshotBeforeUpdate.', 'start': 905.613, 'duration': 3.84}, {'end': 912.374, 'text': 'And that sort of goes right before render.', 'start': 910.354, 'duration': 2.02}, {'end': 925.042, 'text': 'and it takes in previous props in previous state.', 'start': 919.744, 'duration': 5.298}, {'end': 929.083, 'text': 'and then we return a value out of this.', 'start': 927.242, 'duration': 1.841}, {'end': 937.306, 'text': 'This method is to allow us to capture some properties that are not stored in the state before we re-render that component.', 'start': 930.003, 'duration': 7.303}, {'end': 949.891, 'text': "So let's say you had a list view or a text area where the cursor was in a certain row and column, or if the list was scrolled to a certain location,", 'start': 938.066, 'duration': 11.825}], 'summary': 'Lifecycle methods like getsnapshotbeforeupdate capture state changes before re-render.', 'duration': 62.962, 'max_score': 886.929, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c886929.jpg'}, {'end': 1132.008, 'src': 'heatmap', 'start': 1045.7, 'weight': 1, 'content': [{'end': 1058.509, 'text': "so let's call this error component, and we're just going to return a div, with it accessing some non-existent value,", 'start': 1045.7, 'duration': 12.809}, {'end': 1061.737, 'text': 'And this is going to cause it to crash.', 'start': 1060.015, 'duration': 1.722}, {'end': 1063.86, 'text': "So let's say we add it into counter right now.", 'start': 1062.098, 'duration': 1.762}, {'end': 1066.923, 'text': "So I'm going to place that error component here.", 'start': 1064.561, 'duration': 2.362}, {'end': 1072.51, 'text': "When I save, you'll see that there were errors that were triggered here.", 'start': 1067.063, 'duration': 5.447}, {'end': 1079.873, 'text': "Now, if I did not have component at catch, When I save, I lose everything that's rendered in the browser.", 'start': 1073.07, 'duration': 6.803}, {'end': 1090.679, 'text': "And so I could have a downstream component that generates an error and it's not handled properly and it causes the entire app to go into sort of this blank screen.", 'start': 1080.754, 'duration': 9.925}, {'end': 1094.101, 'text': "So that's where ComponentDidCatch comes into the picture.", 'start': 1091.8, 'duration': 2.301}, {'end': 1096.623, 'text': 'It allows us to gracefully handle some of these.', 'start': 1094.742, 'duration': 1.881}, {'end': 1108.64, 'text': "So what I'm going to do is once we know there's an error, we're going to set state and set the error and info properties on it.", 'start': 1097.344, 'duration': 11.296}, {'end': 1112.999, 'text': "And let's handle those here as well and render.", 'start': 1110.077, 'duration': 2.922}, {'end': 1118.881, 'text': "We're going to check for an error being present.", 'start': 1113.299, 'duration': 5.582}, {'end': 1126.545, 'text': "In that case, we're going to return a div that says we have encountered an error.", 'start': 1119.842, 'duration': 6.703}, {'end': 1132.008, 'text': "Let's try to print this out as well.", 'start': 1128.366, 'duration': 3.642}], 'summary': 'Using componentdidcatch to gracefully handle errors and prevent app crashes.', 'duration': 58.938, 'max_score': 1045.7, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c1045700.jpg'}], 'start': 886.929, 'title': 'Component lifecycle and error handling', 'summary': 'Covers the getsnapshotbeforeupdate method for capturing component properties before re-rendering, and the componentdidcatch method for gracefully handling errors in react components, preventing app crashes.', 'chapters': [{'end': 972.482, 'start': 886.929, 'title': 'Component lifecycle methods', 'summary': 'Discusses the getsnapshotbeforeupdate method which captures properties before re-rendering a component, allowing for the handling of details such as cursor position or scroll location, with the returned value being passed into componentdidupdate as a snapshot.', 'duration': 85.553, 'highlights': ['The getSnapshotBeforeUpdate method captures properties before re-rendering a component, allowing for the handling of details such as cursor position or scroll location, with the returned value being passed into componentDidUpdate as a snapshot.', 'This method allows us to capture some properties that are not stored in the state before we re-render that component, which can be useful for scenarios like capturing the cursor position or scroll location.', 'The captured details can be used to handle specific actions later on, such as setting the cursor and caret in a certain place within the DOM.']}, {'end': 1298.261, 'start': 974.923, 'title': 'Handling errors with componentdidcatch', 'summary': 'Discusses the usage of componentdidcatch method as an error boundary to gracefully handle errors in react components, demonstrating how to set error and info properties and conditionally render an error message, preventing the entire app from crashing.', 'duration': 323.338, 'highlights': ['ComponentDidCatch method allows graceful error handling in React components, preventing the entire app from crashing.', 'Usage of error and info parameters to set error properties and conditionally render an error message.', 'Utilizing state attribute to conditionally trigger the showErrorComponent and demonstrating its toggle functionality.', 'Implementing ToggleError method to negate the value of showErrorComponent and using a button to trigger it.']}], 'duration': 411.332, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c886929.jpg', 'highlights': ['The getSnapshotBeforeUpdate method captures properties before re-rendering a component, allowing for the handling of details such as cursor position or scroll location, with the returned value being passed into componentDidUpdate as a snapshot.', 'ComponentDidCatch method allows graceful error handling in React components, preventing the entire app from crashing.', 'This method allows us to capture some properties that are not stored in the state before we re-render that component, which can be useful for scenarios like capturing the cursor position or scroll location.', 'Usage of error and info parameters to set error properties and conditionally render an error message.']}, {'end': 1532.517, 'segs': [{'end': 1332.891, 'src': 'embed', 'start': 1299.061, 'weight': 1, 'content': [{'end': 1300.181, 'text': 'Let me do a quick recap.', 'start': 1299.061, 'duration': 1.12}, {'end': 1309.664, 'text': 'We have the constructor, which is called when a component is created, followed by get derived state from props,', 'start': 1300.822, 'duration': 8.842}, {'end': 1312.685, 'text': 'which allows us to copy props into state.', 'start': 1309.664, 'duration': 3.021}, {'end': 1317.466, 'text': 'This is not used frequently, but there are cases such as this one here,', 'start': 1313.205, 'duration': 4.261}, {'end': 1322.668, 'text': 'where we want to pass in a seed for the counter and have that be controlled internally through the state.', 'start': 1317.466, 'duration': 5.202}, {'end': 1324.248, 'text': "That's when this method is useful.", 'start': 1323.048, 'duration': 1.2}, {'end': 1332.891, 'text': 'We have component did mount, which is also an interesting place to do things like network requests or handle,', 'start': 1324.508, 'duration': 8.383}], 'summary': 'Component lifecycle methods like constructor, get derived state from props, and component did mount are used for specific functionalities such as copying props into state and handling network requests.', 'duration': 33.83, 'max_score': 1299.061, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c1299061.jpg'}, {'end': 1531.757, 'src': 'embed', 'start': 1429.648, 'weight': 0, 'content': [{'end': 1439.234, 'text': 'Anyway, while we were doing the recap, so after component did mount, should component update gets called, this is where we could hint to React.', 'start': 1429.648, 'duration': 9.586}, {'end': 1441.536, 'text': 'do not call render all over again.', 'start': 1439.234, 'duration': 2.302}, {'end': 1444.178, 'text': "I believe in the future that's how the method's going to work.", 'start': 1441.956, 'duration': 2.222}, {'end': 1449.721, 'text': "It's simply going to be a hint, and React will decide if it wants to actually honor that or not.", 'start': 1444.258, 'duration': 5.463}, {'end': 1461.694, 'text': "And there's GetSnapshotBeforeUpdate, which allows us to store things like positions of your list, views or text areas,", 'start': 1451.969, 'duration': 9.725}, {'end': 1469.858, 'text': 'or whatever DOM components that you can then pass on to ComponentDataUpdate and reassign those after the render.', 'start': 1461.694, 'duration': 8.164}, {'end': 1473.42, 'text': 'Render, of course, takes care of rendering content.', 'start': 1471.098, 'duration': 2.322}, {'end': 1477.462, 'text': 'ComponentDataUpdate gets triggered right after render.', 'start': 1474.18, 'duration': 3.282}, {'end': 1480.984, 'text': 'Now, this is also similar to componentDidMount.', 'start': 1478.482, 'duration': 2.502}, {'end': 1490.292, 'text': 'If you wanted to make specific network requests based on certain attributes or props or state values, you could do the same here.', 'start': 1481.565, 'duration': 8.727}, {'end': 1502.662, 'text': "You can actually call setState in componentDidMount, and it triggers a re-render, but it doesn't actually call the render method twice.", 'start': 1491.453, 'duration': 11.209}, {'end': 1506.885, 'text': "It only does it once because of the location where it's called under.", 'start': 1503.582, 'duration': 3.303}, {'end': 1515.489, 'text': 'And finally, this component will unmount that gets triggered when the components removed from the DOM and component did catch,', 'start': 1508.086, 'duration': 7.403}, {'end': 1523.293, 'text': 'which helps us sort of gracefully handle errors in downstream components, lifecycle methods or render method.', 'start': 1515.489, 'duration': 7.804}, {'end': 1525.894, 'text': 'And that brings us to the end of this video.', 'start': 1523.893, 'duration': 2.001}, {'end': 1527.215, 'text': 'Hope it was useful.', 'start': 1526.294, 'duration': 0.921}, {'end': 1531.757, 'text': "And if you'd like to stay up to date with future videos, consider subscribing below.", 'start': 1527.475, 'duration': 4.282}], 'summary': 'Discusses react lifecycle methods, including shouldcomponentupdate, getsnapshotbeforeupdate, componentdidmount, setstate, componentwillunmount, and componentdidcatch.', 'duration': 102.109, 'max_score': 1429.648, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c1429648.jpg'}], 'start': 1299.061, 'title': 'React lifecycle methods', 'summary': 'Covers react lifecycle methods such as constructor, get derived state from props, component did mount, shouldcomponentupdate, getsnapshotbeforeupdate, componentdidupdate, and componentwillunmount, detailing their functionalities in state initialization, network requests handling, data fetching, rendering optimization, and component updates.', 'chapters': [{'end': 1428.597, 'start': 1299.061, 'title': 'Component lifecycle in react', 'summary': 'Discusses the constructor, get derived state from props, and component did mount methods in react, highlighting their use cases and functionality for initializing state, handling network requests, and updating component state based on data fetching.', 'duration': 129.536, 'highlights': ['The component did mount method can be used to handle network requests or the initial loading of the component, such as simulating an initializing state and fetching data with a setTimeout function.', 'The get derived state from props method allows for copying props into state, useful for scenarios like passing a seed for the counter and controlling it internally through state.', "The constructor method is called when a component is created, serving as the initial setup for the component's state and functionality."]}, {'end': 1532.517, 'start': 1429.648, 'title': 'React lifecycle methods overview', 'summary': 'Provides an overview of various react lifecycle methods, including shouldcomponentupdate, getsnapshotbeforeupdate, componentdidupdate, componentdidmount, and componentwillunmount, explaining their roles and how they can be utilized to optimize rendering and handle component updates.', 'duration': 102.869, 'highlights': ['shouldComponentUpdate method being used as a hint to React to prevent unnecessary render calls The shouldComponentUpdate method can be used as a hint to React to prevent unnecessary render calls, potentially optimizing performance by avoiding unnecessary re-renders.', 'GetSnapshotBeforeUpdate method allowing storage of component state before an update The GetSnapshotBeforeUpdate method enables the storage of component state, such as positions of DOM components, before an update, facilitating reassignment of these values after rendering.', 'Explanation of how componentDidMount can be used to make network requests and trigger re-rendering without calling render method twice The video explains how componentDidMount can be utilized to make specific network requests based on attributes, props, or state values, triggering a re-render without invoking the render method twice, thus optimizing the rendering process.', 'Introduction to componentWillUnmount and componentDidCatch for handling component removal and errors respectfully The chapter introduces the componentWillUnmount method, triggered when components are removed from the DOM, and componentDidCatch, which aids in gracefully handling errors in downstream components and the render method.']}], 'duration': 233.456, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/m_mtV4YaI8c/pics/m_mtV4YaI8c1299061.jpg', 'highlights': ['The componentDidMount method can be used to handle network requests or the initial loading of the component, such as simulating an initializing state and fetching data with a setTimeout function.', 'The getDerivedStateFromProps method allows for copying props into state, useful for scenarios like passing a seed for the counter and controlling it internally through state.', "The constructor method is called when a component is created, serving as the initial setup for the component's state and functionality.", 'The shouldComponentUpdate method can be used as a hint to React to prevent unnecessary render calls, potentially optimizing performance by avoiding unnecessary re-renders.', 'The getSnapshotBeforeUpdate method enables the storage of component state, such as positions of DOM components, before an update, facilitating reassignment of these values after rendering.', 'The video explains how componentDidMount can be utilized to make specific network requests based on attributes, props, or state values, triggering a re-render without invoking the render method twice, thus optimizing the rendering process.', 'The chapter introduces the componentWillUnmount method, triggered when components are removed from the DOM, and componentDidCatch, which aids in gracefully handling errors in downstream components and the render method.']}], 'highlights': ['The componentDidMount method can be used to handle network requests or the initial loading of the component, such as simulating an initializing state and fetching data with a setTimeout function.', 'The chapter introduces componentDidMount, a lifecycle method in React components, called after the render, triggering re-rendering.', 'The chapter covers commonly used React lifecycle methods such as componentDidUpdate, componentDidMount, and componentWillUnmount, as well as infrequently used methods like shouldComponentUpdate.', 'The rendering behavior is explained with the addition of markers to denote single render calls and the absence of componentDidMount triggering on incremental render.', 'The componentDidUpdate method takes parameters including previous props, previous date, and snapshot, and is triggered when the component updates.', 'The componentWillUnmount method is called when a component is being taken out of the DOM, and shouldComponentUpdate is used to let React know if render should be triggered, potentially optimizing performance.', 'The getSnapshotBeforeUpdate method captures properties before re-rendering a component, allowing for the handling of details such as cursor position or scroll location, with the returned value being passed into componentDidUpdate as a snapshot.', 'ComponentDidCatch method allows graceful error handling in React components, preventing the entire app from crashing.', "The constructor method is called when a component is created, serving as the initial setup for the component's state and functionality.", 'The shouldComponentUpdate method can be used as a hint to React to prevent unnecessary render calls, potentially optimizing performance by avoiding unnecessary re-renders.']}