Q: Is there a sleep function in JavaScript? Is there a sleep function in JavaScript?

A: You can use the setTimeout or setInterval functions.

A: function sleep(delay) {
    var start = new Date().getTime();
    while (new Date().getTime() < start + delay);
}

This code blocks for the specified duration. This is CPU hogging code. This is different from a thread blocking itself and releasing CPU cycles to be utilized by another thread. No such thing is going on here. Do not use this code, it's a very bad idea.

A: If you are looking to block the execution of code with call to sleep, then no, there is no method for that in JavaScript.
JavaScript does have setTimeout method. setTimeout will let you defer execution of a function for x milliseconds.
setTimeout(myFunction, 3000);

// if you have defined a function named myFunction 
// it will run after 3 seconds (3000 milliseconds)

Remember, this is completely different from how sleep method, if it existed, would behave.
function test1()
{    
    // let's say JavaScript did have a sleep function..
    // sleep for 3 seconds
    sleep(3000);

    alert('hi'); 
}

If you run the above function, you will have to wait for 3 seconds (sleep method call is blocking) before you see the alert 'hi'. Unfortunately, there is no sleep function like that in JavaScript.
function test2()
{
    // defer the execution of anonymous function for 
    // 3 seconds and go to next line of code.
    setTimeout(function(){ 

        alert('hello');
    }, 3000);  

    alert('hi');
}

If you run test2, you will see 'hi' right away (setTimeout is non blocking) and after 3 seconds you will see the alert 'hello'.

A: A naive, CPU-intensive method to block execution for a number of milliseconds:
/**
* Delay for a number of milliseconds
*/
function sleep(delay) {
    var start = new Date().getTime();
    while (new Date().getTime() < start + delay);
}

