Every React Concept Explained in 12 Minutes

00:11:52
https://www.youtube.com/watch?v=wIyHSOugGGw

摘要

TLDRThe video dives into the fundamental concepts of React, detailing its components, which are like building blocks for React applications, allowing developers to construct UI parts like buttons and pages with reusable code blocks that are JavaScript functions returning JSX (JavaScript XML). JSX is preferred over the alternative createElement function for writing UI because it integrates JavaScript with XML-like syntax. Attributes in JSX are written in camel case to incorporate JavaScript values, enabling dynamic updates and styles. Using props enables data passing between components, which include custom attributes to make React layouts more organized, leveraging the children prop for component composition. State management, central to React applications, is optimized with hooks like useState and useReducer. These hooks manage state changes efficiently, triggering re-renders when data changes. The virtual DOM, another key feature, facilitates quick updating and rendering by minimizing direct DOM manipulations, applying processes like diffing and reconciliation to keep UI performance high. Error boundaries and suspense are also explored, aiding in error handling and managing asynchronous data loads, respectively.

心得

  • 🔧 React components are reusable JavaScript functions that return JSX.
  • 📜 JSX is a syntax extension that looks like HTML but works with JavaScript.
  • 🚀 Props allow data to flow between components, enhancing modularity.
  • 📊 State management is handled using hooks like useState and useReducer.
  • 🌳 React utilizes a virtual DOM for efficient rendering.
  • ⚠️ Error boundaries catch and manage rendering errors gracefully.
  • 🌍 Hooks like useEffect and useContext integrate with external systems.
  • 🔗 Controlled components offer predictable behavior using state.
  • 🔍 The key prop uniquely identifies elements in lists for stable rendering.
  • ⏳ Suspense provides user feedback during component laziness loading.

时间轴

  • 00:00:00 - 00:05:00

    React is a JavaScript library that relies on components, which are the building blocks for creating user interfaces. Components are reusable pieces of code that return JSX, a syntax extension that resembles HTML but behaves like JavaScript. JSX allows for dynamic content and styling using JavaScript objects. To pass data between components, React uses props, which function like custom attributes. The children prop aids in composition by allowing components to have nested children. React’s rendering process involves updating the virtual DOM, diffing changes, and reconciling them to the real DOM. Key props identify components uniquely during lists rendering, preventing potential render issues.

  • 00:05:00 - 00:11:52

    State in React manages app data and determines when components render. It is manipulated using hooks like useState, which returns a state variable and a setter function. Controlled components use state to control input values, providing predictable behavior. React hooks like useEffect and useRef extend functionalities to handle side effects and reference DOM elements directly. Context avoids prop drilling by providing a way to share data at different component levels without passing props through every layer. Portals allow rendering components outside their parent’s hierarchy, ideal for UI elements like modals. Suspense provides fallbacks during component loading. Error boundaries handle app-breaking errors, offering users a fail-safe message. Developers can start mastering React concepts further through a detailed bootcamp.

思维导图

Mind Map

常见问题

  • What are React components?

    React components are the building blocks of React apps, allowing you to create visible parts like buttons and pages.

  • What is JSX in React?

    JSX is a syntax extension for JavaScript used in React, allowing you to write markup-like syntax.

  • How does React manage dynamic data?

    React uses state and props to manage dynamic data, allowing components to update and display changes effectively.

  • What is the purpose of React's virtual DOM?

    The virtual DOM in React improves performance by updating changes efficiently without affecting the real DOM directly.

  • What are React hooks?

    Hooks in React are functions that let you use state and other features in functional components.

  • What is the use of the 'useState' hook?

    The 'useState' hook allows you to add state to functional components, managing data that changes over time.

  • How are error boundaries used in React?

    Error boundaries in React catch errors during rendering and display fallback UI instead of crashing the whole app.

  • What is React's 'strict mode'?

    Strict mode in React is used to identify potential problems in an application during development.

  • What are props in React?

    Props are custom attributes passed to React components for data transfer between components.

  • What is suspense in React?

    Suspense in React is used to show fallback UI like spinners while waiting for components to load asynchronous data.

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  • 00:00:00
    react is a JavaScript library full of
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    fancy terms like reconciliation
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    composition and error boundaries what do
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    all these terms actually mean let's
  • 00:00:09
    start from the beginning with components
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    components are the building blocks of
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    every react app they allow us to make
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    all the visible parts of our
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    applications like buttons inputs or even
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    entire Pages just like Legos you can use
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    components as many times as you want
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    every react component is a JavaScript
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    function that returns markup but since
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    react is is a JavaScript library react
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    components don't return HTML markup they
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    actually return something called jsx
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    which is Javascript in Disguise jsx is
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    optional but the alternative way to make
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    user interfaces is with the function
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    create element which gets annoying to
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    write pretty fast so everyone just uses
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    jsx since jsx is Javascript you can't
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    write attributes like you would in HTML
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    you have to write them in the camel case
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    style that means HTML attributes like
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    class become class name unlike HTML
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    which is static and unchanging the
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    benefit of using react is that you can
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    use Dynamic JavaScript values in your
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    jsx if you have data you can display it
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    in your jsx using curly braces curly
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    braces accept values like strings and
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    numbers directly you can use them to
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    make your attributes Dynamic and you can
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    style react elements using a JavaScript
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    object within the curly braces since
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    JavaScript functions can only return one
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    thing in react you can only return one
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    parent element from a component so you
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    can't do this without getting a big
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    error we could fix this by wrapping
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    these components in a div but maybe you
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    don't want to add another element to the
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    page instead you can use an empty
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    component called a react fragment okay
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    but what if I want to pass data into
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    another component for that you use
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    something called props to make a prop
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    create a name on the component you want
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    to pass data to and set it equal to some
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    value and that's it you can then use
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    that prop in the component you passed it
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    to props refers to properties on an
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    object which is what you get in the
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    parameters of each component to use the
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    prop take it from the object like a
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    normal JavaScript property think of them
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    like custom attributes you can add to
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    any component so wait can you pass
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    anything as a prop yes you can you can
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    even pass other components as props
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    using the children prop if you make
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    opening and closing tags for a component
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    you can pass other components in between
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    them these pass components are called
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    children and you can access them on the
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    children promp of the parent component
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    and it's great for something called
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    composition which is about organizing
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    our react components in the most optimal
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    way the children prop is really useful
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    for creating layout components when you
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    want your children to have the same
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    common layout the key prop is another
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    built-in prop to react and no unlike the
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    name implies it doesn't unlock anything
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    interesting the key prop is used so
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    react can tell one component apart from
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    another usually when you're creating a
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    list with the map function a key is just
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    a unique string or number to identify a
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    component you'll usually know when you
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    need to add a key because react will
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    warn you in the console fortunately if
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    you don't have a unique value for each
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    item you can always use the current
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    index from the map function but how does
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    react take all my amazing code and make
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    it display something in the browser that
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    process is called rendering react does
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    this for us but it's important to know
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    how it works because sometimes we can do
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    a bad thing and cause it to infinitely
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    reender which crashes our app the way
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    react knows how and when to render our
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    application is using something called
  • 00:03:50
    the virtual Dom also known as the vdom
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    okay but what does Dom mean Dom stands
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    for document object model which is what
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    every browser uses to model all the HTML
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    elements on a web page and when you draw
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    it out it kind of looks like a tree
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    here's the complete rendering process in
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    react if the state of our react app
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    changes then react updates the virtual
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    Dom which is quicker to update than the
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    real Dom then react uses a process
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    called diffing to compare the updated
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    virtual Dom to a previous version to see
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    what's changed once it sees what's
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    different react uses a process called
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    reconcil iation to update the real Dom
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    with the changes that it found whenever
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    someone uses our app tons of events take
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    place like clicks Mouse movements and
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    key presses many of which we need to
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    detect event handling is how we take
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    those user events and do something with
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    them react has a lot of built-in events
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    such as onclick onchange and onsubmit
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    these three events are ones you'll
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    probably use the most if we want to
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    alert users when a button is clicked we
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    would add the onclick prop to the button
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    and connect it to a function that would
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    show that
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    alert to manage data in our react apps
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    we need to use State not that kind of
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    state though state is like a snapshot
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    from a camera it's a picture of our app
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    at any given time to manage State we
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    also can't use JavaScript variables they
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    don't cause our app to render instead we
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    use special functions like use State and
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    use reducer use State takes an argument
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    that serves as the starting value value
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    of the state variable which is likes in
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    this example and returns an array
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    containing the state variable and a
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    function to update that state using our
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    button example we could also update the
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    number of times the button's been
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    clicked with the update function set
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    clicks and display it in the button with
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    the state variable
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    likes controlled components use State
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    values to have more predictable Behavior
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    here's an example of a controlled
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    component where the value typed into the
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    input is being put into State and
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    controlled by the state variable value
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    here's how it works the user types and
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    set value puts what the user typed into
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    State the state value is then updated
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    and finally the input uses that updated
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    State as its value controlled components
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    are a great pattern to use because if we
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    want to change the component's behavior
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    we just need to change the state that
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    controls it UST state is an example of a
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    react hook which allow us to hook into
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    features such as state within function
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    components there are five main types of
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    hooks State hooks like use State and use
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    reducer help you manage state within
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    react components context hooks such as
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    use context let you Ed data pass through
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    react context ref hooks such as use ref
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    let you reference things like HTML
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    elements effect hooks like use effect
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    let you connect with external systems
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    like browser apis and performance hooks
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    like use memo and use callback which can
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    improve performance by preventing
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    unnecessary work you'll use all of these
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    hooks at some point but the majority of
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    the time you'll likely use just three
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    hooks in your react components use State
  • 00:07:18
    use effect and use ref when you think of
  • 00:07:21
    the word purity you might think of
  • 00:07:23
    something like purified water Purity is
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    a term used to describe how react
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    components should work work but this
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    type of Purity is more like how
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    mathematical formulas are pure pure
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    react components mean that the same
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    input should always return the same
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    output to keep a react component pure
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    they should only return their jsx and
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    not change any objects or variables that
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    existed before rendering the cup
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    component in this example is impure
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    because it changes the variable count
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    during render which exists outside the
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    component this leads to the jsx have
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    having the wrong output when it is used
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    more than once to help make sure we
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    don't run into errors like this we can
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    use something called strict mode strict
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    mode is a special component which tells
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    us about mistakes as we develop our
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    react apps it's really convenient
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    because it's just a component we usually
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    wrap around our app component and it'll
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    tell us when we really shouldn't do
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    something but what if we need to do
  • 00:08:23
    something outside our react app your app
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    might need to talk with the browser API
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    or make a request to a server if you do
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    have an external system you're going to
  • 00:08:33
    need a way to step outside of react
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    effects are code that reach outside of
  • 00:08:38
    our react application usually effects
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    also known as side effects can be done
  • 00:08:43
    within event handlers for example to
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    make an HTTP request when you submit a
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    form or click on a button if you can't
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    run your effects within an event handler
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    then you can run them using the use
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    effect hook for example a common pattern
  • 00:08:58
    is to fetch dat data when components
  • 00:09:00
    first load with the use effect hook like
  • 00:09:04
    effects sometimes you want to step
  • 00:09:05
    outside react and work directly with the
  • 00:09:08
    Dom to reference an actual Dom element
  • 00:09:11
    you can use what's called a ref you can
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    create a ref with the Ed ref hook and to
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    get access to a Dom element use the ref
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    prop on any react element for some tasks
  • 00:09:22
    such as focusing an input it's much
  • 00:09:24
    easier to reference the actual Dom
  • 00:09:26
    element instead of attempting to do it
  • 00:09:28
    the react way
  • 00:09:30
    context is a powerful way to pass prop
  • 00:09:32
    data through your apps components most
  • 00:09:35
    react apps have tons of nested
  • 00:09:37
    components to get data down multiple
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    levels involves passing the same props
  • 00:09:42
    through components that don't actually
  • 00:09:44
    need it context lets us jump through the
  • 00:09:47
    component tree and use data at any level
  • 00:09:49
    without making props to use context you
  • 00:09:52
    first create context in a parent
  • 00:09:55
    component then wrap your parent
  • 00:09:57
    component in a special context component
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    called a context provider put the data
  • 00:10:02
    you want to pass down on the provider
  • 00:10:05
    and finally access that data in any
  • 00:10:07
    child component with the used context
  • 00:10:10
    hook portals on the other hand are kind
  • 00:10:13
    of like context but for components
  • 00:10:15
    portals let you move react components
  • 00:10:17
    into any HTML element you select portals
  • 00:10:21
    are great for components that can't be
  • 00:10:22
    displayed properly because of their
  • 00:10:24
    parents component styles for example for
  • 00:10:26
    displaying modals drop-down menus and
  • 00:10:29
    tool tips to create a portal just use
  • 00:10:32
    the create portal function pass your
  • 00:10:34
    component to it and choose the HTML
  • 00:10:37
    element where you'd like your react
  • 00:10:39
    component to appear suspense is a
  • 00:10:41
    special component that helps you handle
  • 00:10:43
    loading a component or its data suspense
  • 00:10:46
    is helpful for components that take some
  • 00:10:48
    time to fetch data it provides a better
  • 00:10:51
    user experience to show a fallback
  • 00:10:53
    component like a loading spinner until
  • 00:10:55
    the data is available instead of nothing
  • 00:10:58
    suspense is also useful if you're lazily
  • 00:11:00
    loading a component which lets us load a
  • 00:11:03
    component only when it's needed since
  • 00:11:06
    react apps are all JavaScript errors
  • 00:11:08
    that happen during rendering can totally
  • 00:11:10
    break your app airor boundaries are
  • 00:11:12
    components that let you catch app
  • 00:11:14
    breaking errors and show a fallback
  • 00:11:16
    component to tell the user about what
  • 00:11:18
    happened for example our app will crash
  • 00:11:21
    if we run this code because it throws an
  • 00:11:23
    error when there's no user to prevent
  • 00:11:25
    our app from crashing we'll first add an
  • 00:11:28
    error boundary to display a fallback
  • 00:11:30
    component with a more helpful error
  • 00:11:32
    message to be displayed to the user now
  • 00:11:35
    if you really want to dive deep into
  • 00:11:37
    react I've put together a complete boot
  • 00:11:40
    camp to help you master every one of
  • 00:11:41
    these Concepts from front to back you
  • 00:11:44
    can get started now at react boot camp.
  • 00:11:47
    I hope you learned a lot in this video
  • 00:11:49
    and I'll see you in the next one
标签
  • React
  • JavaScript
  • Components
  • JSX
  • Props
  • State
  • Hooks
  • Virtual DOM
  • Error Boundaries
  • Suspense