Execute script after specific delay using JavaScript

Just to add to what everyone else have said about setTimeout: If you want to call a function with a parameter in the future, you need to set up some anonymous function calls.

You need to pass the function as an argument for it to be called later. In effect this means without brackets behind the name. The following will call the alert at once, and it will display 'Hello world':

var a = "world";
setTimeout(alert("Hello " + a), 2000);

To fix this you can either put the name of a function (as Flubba has done) or you can use an anonymous function. If you need to pass a parameter, then you have to use an anonymous function.

var a = "world";
setTimeout(function(){alert("Hello " + a)}, 2000);
a = "Stack Overflow";

But if you run that code you will notice that after 2 seconds the popup will say 'Hello Stack Overflow'. This is because the value of the variable a has changed in those two seconds. To get it to say 'Hello world' after two seconds, you need to use the following code snippet:

function callback(a){
    return function(){
        alert("Hello " + a);
    }
}
var a = "world";
setTimeout(callback(a), 2000);
a = "Stack Overflow";

It will wait 2 seconds and then popup 'Hello world'.

There is the following:

setTimeout(function, milliseconds);

function which can be passed the time after which the function will be executed.

See: Window setTimeout() Method.

Just to expand a little... You can execute code directly in the setTimeout call, but as @patrick says, you normally assign a callback function, like this. The time is milliseconds

setTimeout(func, 4000);
function func() {
    alert('Do stuff here');
}

You need to use setTimeout and pass it a callback function. The reason you can't use sleep in javascript is because you'd block the entire page from doing anything in the meantime. Not a good plan. Use Javascript's event model and stay happy. Don't fight it!

You can also use window.setInterval() to run some code repeatedly at a regular interval.

I really liked Maurius' explanation (highest upvoted response) with the three different methods for calling setTimeout.

In my code I want to automatically auto-navigate to the previous page upon completion of an AJAX save event. The completion of the save event has a slight animation in the CSS indicating the save was successful.

In my code I found a difference between the first two examples:

setTimeout(window.history.back(), 3000);

This one does not wait for the timeout--the back() is called almost immediately no matter what number I put in for the delay.

However, changing this to:

setTimeout(function() {window.history.back()}, 3000);

This does exactly what I was hoping.

This is not specific to the back() operation, the same happens with alert(). Basically with the alert() used in the first case, the delay time is ignored. When I dismiss the popup the animation for the CSS continues.

Thus, I would recommend the second or third method he describes even if you are using built in functions and not using arguments.

delay function:

/**
 * delay or pause for some time
 * @param {number} t - time (ms)
 * @return {Promise<*>}
 */
const delay = async t => new Promise(resolve => setTimeout(resolve, t));

usage inside async function:

await delay(1000);

Or

delay(1000).then(() => {
   // your code...
});

Or without a function

new Promise(r => setTimeout(r, 1000)).then(() => {
   // your code ...
});
// or
await new Promise(r => setTimeout(r, 1000));
// your code...

As other said, setTimeout is your safest bet
But sometimes you cannot separate the logic to a new function then you can use Date.now() to get milliseconds and do the delay yourself....

function delay(milisecondDelay) {
   milisecondDelay += Date.now();
   while(Date.now() < milisecondDelay){}
}

alert('Ill be back in 5 sec after you click OK....');
delay(5000);
alert('# Im back # date:' +new Date());

The simplest solution to call your function with delay is:

function executeWithDelay(anotherFunction) {
    setTimeout(anotherFunction, delayInMilliseconds);
}