I just want to get the return value from setTimeout but what I get is a whole text format of the function?
function x () {
setTimeout(y = function () {
return 'done';
}, 1000);
return y;
}
console.log(x());
asked Jul 24, 2014 at 8:35
5 Answers
You need to use Promises for this. They are available in ES6 but can be polyfilled quite easily:
function x() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve('done!');
});
});
}
x().then((done) => {
console.log(done); // --> 'done!'
});
With async/await in ES2017 it becomes nicer if inside an async function:
async function() {
const result = await x();
console.log(result); // --> 'done!';
}
answered Jul 24, 2014 at 8:49
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actually the
donein my example was a promise that needs to be returned inside a setTimeout..because i cant get the returned deferred.resolve() inside setTimeout. how would it be? thank you Commented Jul 24, 2014 at 9:33 -
8Can you post a clearer example of your code in the question? Commented Jul 24, 2014 at 11:11
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It is better if you don't identify the argument passed to the function called by bind as done, some people may find it confusing as there is a string with bind above. x().then((promisedValue) => { console.log(promisedValue)}); // --> 'done!' Something like this.– gabs1bb3Commented Jun 10 at 13:11
You can't get a return value from the function you pass to setTimeout.
The function that called setTimeout (x in your example) will finish executing and return before the function you pass to setTimeout is even called.
Whatever you want to do with the value you get, you need to do it from the function you pass to setTimeout.
In your example, that would be written as:
function x () {
setTimeout(function () {
console.log("done");
}, 1000);
}
x();
answered Jul 24, 2014 at 8:38
Better to take a callback for function x and whatever task you want to perform after that timeout send in that callback.
function x (callback) {
setTimeout(function () {
callback("done");
}, 1000);
}
x(console.log.bind(console)); //this is special case of console.log
x(alert)
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2Bare in mind, that this will not await after the function call, so it might actually not happen. For example add process.exit, after calling x and "done" will be never done. Commented Oct 30, 2018 at 8:42
You can use a combination of Promise and setTimeOut like the example below
let f1 = function(){
return new Promise(async function(res,err){
let x=0;
let p = new Promise(function(res,err){
setTimeout(function(){
x= 1;
res(x);
},2000)
})
p.then(function(x){
console.log(x);
res(x);
})
});
}
I think you want have flag to know event occured or no. setTimeout not return a value. you can use a variable to detect event occured or no
var y="notdone";
setTimeout(function () {
y="done";
}, 1000);
You can access variable y after timeout occured to know done or not
xand call that function with done.const x = async (waitMs) => new Promise((resolve) => setTimeout(() => resolve('done'), waitMs));console.log(await x(1000));