Syntax for an async arrow function

I can mark a JavaScript function as "async" (i.e., returning a promise) with the async keyword. Like this:

async function foo() { // Do something } 

What is the equivalent syntax for arrow functions?

8 Answers

Async arrow functions look like this:

const foo = async () => { // do something } 

Async arrow functions look like this for a single argument passed to it:

const foo = async evt => { // do something with evt } 

Async arrow functions look like this for multiple arguments passed to it:

const foo = async (evt, callback) => { // do something with evt // return response with callback } 

The anonymous form works as well:

const foo = async function() { // do something } 

An async function declaration looks like this:

async function foo() { // do something } 

Using async function in a callback:

const foo = event.onCall(async () => { // do something }) 

Using async method inside of a class:

async foo() { // do something } 

This the simplest way to assign an async arrow function expression to a named variable:

const foo = async () => { // do something } 

_{(Note that this is not strictly equivalent to async function foo() { }. Besides the differences between the function keyword and an arrow expression, the function in this answer is not "hoisted to the top".)}

Immediately Invoked Async Arrow Function:

(async () => { console.log(await asyncFunction()); })(); 

Immediately Invoked Async Function Expression:

(async function () { console.log(await asyncFunction()); })(); 

Async Arrow function syntax with parameters

const myFunction = async (a, b, c) => { // Code here } 

Basic Example

folder = async () => { let fold = await getFold(); //await localStorage.save('folder'); return fold; }; 

async function foo() { // do something } 

Is equivalent to:

const foo = async () => { // do something } 

Calling foo with one argument like in the following example:

async function foo(arg1) { // do something } 

Is equivalent to calling foo like this (both ways are acceptable since parentheses are optional but not required when just one argument is provided)

const foo = async arg1 => { // do something } const foo = async (arg1) => { // do something } 

if you call foo with two or more arguments

async function foo(arg1, arg2) { // do something } 

Is equivalent to: (parentheses are now required)

 const foo = async (arg1, arg2) => { // do something } 

And for a practical example with an await use inside:

const foo = async () => await Promise.resolve('done'); 

You may also do:

 YourAsyncFunctionName = async (value) => { /* Code goes here */ } 

My async function

const getAllRedis = async (key) => { let obj = []; await client.hgetall(key, (err, object) => { console.log(object); _.map(object, (ob)=>{ obj.push(JSON.parse(ob)); }) return obj; // res.send(obj); }); }