Explain the purpose of render in ReactJS

If you try to call this on a component that has not been mounted yet (like calling findDOMNode() in render() on a component that has yet to be created) an exception will be thrown. Remove a mounted React component from the DOM and clean up its event handlers and state. If no component was mounted in the container, calling this function does nothing. Returns true if a component was unmounted and false if there was no component to unmount.

A functional component’s “Return” statement determines what should be presented on the screen, whereas the “Render” method is used to specify how a component displays in terms of UI elements. When investigating the full-stack web development area, consider the minute variations between ReactJS’s Render and Return techniques. The Render method grants a single child component meant to be displayed by its parent. The Return method, in contrast, refuses to accept any provided value to Return to its invoker. When a component renders to null or false, findDOMNode returns null. When a component renders to a string, findDOMNode returns a text DOM node containing that value.

Explain the purpose of render() in ReactJS

The react-dom package provides DOM-specific methods that can be used at the top level of your app and as an escape hatch to get outside the React model if you need to. The render() function has access to the component instance via this. The second parameter to setState() is an optional callback function that will be executed once setState is completed and the component is re-rendered. Generally we recommend using componentDidUpdate() for such logic instead.

Only use error boundaries for recovering from unexpected exceptions; don’t try to use them for control flow. Constructor is the only place where you should assign this.state uses of rendering directly. Fullstack web developer, freelancer, content creator, and indie hacker. Building SaaS products to profitability and creating content about tech & SaaS.

What is Render in React JS?

In this article, we discussed the various concepts of Render using React.JS with examples. VDOM determines, as a Virtual “Document object Model library”, that it Displays instances in the UI with the help of defined certain logic. React supports all modern browsers, although some polyfills are required for older versions. As we can see, h can work with components imported from any file format as long as it’s a valid Vue component.

• In the rare case that you need to force the DOM update to be applied synchronously, you may wrap it in flushSync, but this may hurt performance.
• Note that this method is fired on every render, regardless of the cause.
• It is used to display the component on the UI returned as HTML or JSX components.

A class component becomes an error boundary if it defines either (or both) of the lifecycle methods static getDerivedStateFromError() or componentDidCatch(). Updating state from these lifecycles lets you capture an unhandled JavaScript error in the below tree and display a fallback UI. GetSnapshotBeforeUpdate() is invoked right before the most recently rendered output is committed to e.g. the DOM. It enables your component to capture some information from the DOM (e.g. scroll position) before it is potentially changed. Any value returned by this lifecycle method will be passed as a parameter to componentDidUpdate(). If you’d like, you can reuse some code between getDerivedStateFromProps() and the other class methods by extracting pure functions of the component props and state outside the class definition.

Rendering an Element Using the DOM

Normally you should try to avoid all uses of forceUpdate() and only read from this.props and this.state in render(). Typically, this method can be replaced by componentDidUpdate(). If you were reading from the DOM in this method (e.g. to save a scroll position), you can move that logic to getSnapshotBeforeUpdate(). On production, instead, the errors will not bubble up, which means any ancestor error handler will only receive errors not explicitly caught by componentDidCatch().

H() is short for hyperscript – which means “JavaScript that produces HTML (hypertext markup language)”. This name is inherited from conventions shared by many virtual DOM implementations. A more descriptive name could be createVnode(), but a shorter name helps when you have to call this function many times in a render function. If you are new to the concept of virtual DOM and render functions, make sure to read the Rendering Mechanism chapter first. Sometimes when the stateful data changes its value and some subsequent API calls are made after the first render has invoked, componentDidUpdate() is used.

render()

This method is useful for reading values out of the DOM, such as form field values and performing DOM measurements. In most cases, you can attach a ref to the DOM node and avoid using findDOMNode at all. Render() controls the contents of the container node you pass in. Any existing DOM elements inside are replaced when first called. Later calls use React’s DOM diffing algorithm for efficient updates.

For instance, it is advised to favor the Render method when the requirement to yield numerous values from a function occurs. Furthermore, let’s say you run into a circumstance where you need to call a function that isn’t part of the same component. The best course of action in that situation is to use the lifecycle rather than the Return method. FindDOMNode only works on mounted components (that is, components that have been placed in the DOM).

The talk delves deeply into these two strategies, thoroughly examining them and providing information on the difference between Render and Return methods in ReactJS. Continue reading to learn more about the operational details for practical implementation, whether you’re beginning a React development journey or honing an existing ability with a React JS tutorial. FlushSync may also flush updates outside the callback when necessary to flush the updates inside the callback. For example, if there are pending updates from a click, React may flush those before flushing the updates inside the callback.

If the props option is not specified, then the props object passed to the function will contain all attributes, the same as attrs. The prop names will not be normalized to camelCase unless the props option is specified. GetDerivedStateFromError() is called during the “render” phase, so side-effects are not permitted. Note that this method is fired on every render, regardless of the cause. This is in contrast to UNSAFE_componentWillReceiveProps, which only fires when the parent causes a re-render and not as a result of a local setState.

Render vs. Return Methods in React

Do not rely on it to “prevent” a rendering, as this can lead to bugs. Consider using the built-in PureComponent instead of writing shouldComponentUpdate() by hand. PureComponent performs a shallow comparison of props and state, and reduces the chance that you’ll skip a necessary update. The render() function should be pure, meaning that it does not modify component state, it returns the same result each time it’s invoked, and it does not directly interact with the browser. If your project really just needs one rendering method specifically, you can also reach for a simpler framework that caters to just that. So, it’s good to consider whether the setup and configuration work is going to be worthwhile for the features it unlocks, or if a simpler solution really suffices.