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JavaScript syntax extension
JSX (sometimes referred to as JavaScript XML) is an XML-like extension to the JavaScript language syntax.[1] Initially created by Facebook for use with React, JSX has been adopted by multiple web frameworks.[2]: 5 [3]: 11 Being a syntactic sugar, JSX is generally transpiled into nested JavaScript function calls structurally similar to the original JSX.
An example of JSX code:
const App = () => {
return (
<div>
<p>Header</p>
<p>Content</p>
<p>Footer</p>
</div>
);
}
Multiple elements on the same level need to be wrapped in a single React element such as the <div> element shown above, a fragment delineated by <Fragment> or in its shorthand form <>, or returned as an array.[4][5][3]: 68–69
JSX provides a range of element attributes designed to mirror those provided by HTML. Custom attributes can also be passed to the component.[6] All attributes will be received by the component as props.
JavaScript expressions[edit]JavaScript expressions (but not statements) can be used inside JSX with curly brackets {}:[3]: 14–16
The example above will render:
Conditional expressions[edit]If–else statements cannot be used inside JSX but conditional expressions can be used instead. The example below will render { i === 1 ? 'true' : 'false' } as the string 'true' because i is equal to 1.
const App = () => {
const i = 1;
return (
<div>
<h1>{ i === 1 ? 'true' : 'false' }</h1>
</div>
);
}
The above will render:
<div> <h1>true</h1> </div>
Functions and JSX can be used in conditionals:[3]: 88–90
const App = () => {
const sections = [1, 2, 3];
return (
<div>
{sections.map((n,i) => (
/* 'key' is used by React to keep track of list items and their changes */
/* Each 'key' must be unique */
<div key={"section-" + n}>
Section {n} {i === 0 && <span>(first)</span>}
</div>
))}
</div>
);
}
The above will render:
<div> <div>Section 1<span>(first)</span></div> <div>Section 2</div> <div>Section 3</div> </div>
Code written in JSX requires conversion with a tool such as Babel before it can be understood by web browsers.[7][8]: 5 This processing is generally performed during a software build process before the application is deployed.
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