freeCodeCamp/guide/english/javascript/window-settimeout-method/index.md

title
Window setTimeout Method

Window setTimeout Method

The setTimeout() method calls a function or evaluates an expression after a specified number of milliseconds.

Tips:

• 1000 ms = 1 second.
• The function is only executed once. If you need to repeat execution, use the setInterval() method.
• Use the clearTimeout() method to prevent the function from running.

The syntax of the setTimout() method is as follows:

setTimeout(function, milliseconds, param1, param2, ...);

For example:

setTimeout(function(){ alert("Hello"); }, 3000);

A very important thing about setTimeout() is that it will be executed asynchronously. Let's take an example:

console.log("A");
setTimeout(function(){ console.log("B"); }, 0);
console.log("C");
// The order in the console will be
// A
// C
// B

Not as exepected! But we specify only 0 seconds!!! To solve this problem and make sure that our code will execute synchronously we have just to nest the last console in the function

console.log("A");
setTimeout(function() {
    console.log("B");
    console.log("C");
}, 0);
// The order in the console will be
// A
// B
// C

More Information:

Documentation: MDN

More examples of setTimeout function: w3schools

To understand what really happen under the hood just watch this awesome video Philip Roberts: What the heck is the event loop anyway? | JSConf EU 2014