The async function
keyword can be used to define async
functions inside expressions.
You can also define async functions using an async function statement.
The async function
keyword can be used to define async
functions inside expressions.
You can also define async functions using an async function statement.
async function [name]([param1[, param2[, ..., paramN]]]) { statements }
As of ES2015, you can also use arrow functions.
name
The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
paramN
The name of an argument to be passed to the function.
statements
The statements which comprise the body of the function.
An async function
expression is very similar to, and has almost the same syntax as, an async function statement
. The main difference between an async function
expression and an async function
statement is the function name, which can be omitted in async function
expressions to create anonymous functions. An async function
expression can be used as an IIFE (Immediately Invoked Function Expression) which runs as soon as it is defined. See also the chapter about functions for more information.
function resolveAfter2Seconds(x) { return new Promise(resolve => { setTimeout(() => { resolve(x); }, 2000); }); }; const add = async function(x) { // async function expression assigned to a variable let a = await resolveAfter2Seconds(20); let b = await resolveAfter2Seconds(30); return x + a + b; }; add(10).then(v => { console.log(v); // prints 60 after 4 seconds. }); (async function(x) { // async function expression used as an IIFE let p_a = resolveAfter2Seconds(20); let p_b = resolveAfter2Seconds(30); return x + await p_a + await p_b; })(10).then(v => { console.log(v); // prints 60 after 2 seconds. });
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async_function |
55
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15
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52
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No
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42
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10.1
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55
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55
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52
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42
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10.3
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6.0
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1.0
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7.6.0
7.0.0
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async function
AsyncFunction
objectawait
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/async_function