Javascript do after time

setInterval() global function

The setInterval() method, offered on the Window and Worker interfaces, repeatedly calls a function or executes a code snippet, with a fixed time delay between each call.

This method returns an interval ID which uniquely identifies the interval, so you can remove it later by calling clearInterval() .

Syntax

setInterval(code) setInterval(code, delay) setInterval(func) setInterval(func, delay) setInterval(func, delay, arg0) setInterval(func, delay, arg0, arg1) setInterval(func, delay, arg0, arg1, /* … ,*/ argN) 

Parameters

A function to be executed every delay milliseconds. The first execution happens after delay milliseconds.

An optional syntax allows you to include a string instead of a function, which is compiled and executed every delay milliseconds. This syntax is not recommended for the same reasons that make using eval() a security risk.

The time, in milliseconds (thousandths of a second), the timer should delay in between executions of the specified function or code. Defaults to 0 if not specified. See Delay restrictions below for details on the permitted range of delay values.

Additional arguments which are passed through to the function specified by func once the timer expires.

Return value

The returned intervalID is a numeric, non-zero value which identifies the timer created by the call to setInterval() ; this value can be passed to clearInterval() to cancel the interval.

It may be helpful to be aware that setInterval() and setTimeout() share the same pool of IDs, and that clearInterval() and clearTimeout() can technically be used interchangeably. For clarity, however, you should try to always match them to avoid confusion when maintaining your code.

Note: The delay argument is converted to a signed 32-bit integer. This effectively limits delay to 2147483647 ms, since it’s specified as a signed integer in the IDL.

Examples

Example 1: Basic syntax

The following example demonstrates setInterval() ‘s basic syntax.

const intervalID = setInterval(myCallback, 500, "Parameter 1", "Parameter 2"); function myCallback(a, b)  // Your code here // Parameters are purely optional. console.log(a); console.log(b); > 

Example 2: Alternating two colors

The following example calls the flashtext() function once a second until the Stop button is pressed.

HTML

div id="my_box"> h3>Hello Worldh3> div> button id="start">Startbutton> button id="stop">Stopbutton> 

CSS

.go  color: green; > .stop  color: red; > 

JavaScript

// variable to store our intervalID let nIntervId; function changeColor()  // check if an interval has already been set up if (!nIntervId)  nIntervId = setInterval(flashText, 1000); > > function flashText()  const oElem = document.getElementById("my_box"); oElem.className = oElem.className === "go" ? "stop" : "go"; > function stopTextColor()  clearInterval(nIntervId); // release our intervalID from the variable nIntervId = null; > document.getElementById("start").addEventListener("click", changeColor); document.getElementById("stop").addEventListener("click", stopTextColor); 

Result

The «this» problem

When you pass a method to setInterval() or any other function, it is invoked with the wrong this value. This problem is explained in detail in the JavaScript reference.

Explanation

Code executed by setInterval() runs in a separate execution context than the function from which it was called. As a consequence, the this keyword for the called function is set to the window (or global ) object, it is not the same as the this value for the function that called setTimeout . See the following example (which uses setTimeout() instead of setInterval() – the problem, in fact, is the same for both timers):

= ["zero", "one", "two"]; myArray.myMethod = function (sProperty)  alert(arguments.length > 0 ? this[sProperty] : this); >; myArray.myMethod(); // prints "zero,one,two" myArray.myMethod(1); // prints "one" setTimeout(myArray.myMethod, 1000); // prints "[object Window]" after 1 second setTimeout(myArray.myMethod, 1500, "1"); // prints "undefined" after 1,5 seconds // Passing the 'this' object with .call won't work // because this will change the value of this inside setTimeout itself // while we want to change the value of this inside myArray.myMethod. // In fact, it will be an error because setTimeout code expects this to be the window object: setTimeout.call(myArray, myArray.myMethod, 2000); // error: "NS_ERROR_XPC_BAD_OP_ON_WN_PROTO: Illegal operation on WrappedNative prototype object" setTimeout.call(myArray, myArray.myMethod, 2500, 2); // same error 

As you can see there are no ways to pass the this object to the callback function in the legacy JavaScript.

A possible solution

All modern JavaScript runtimes (in browsers and elsewhere) support arrow functions, with lexical this — allowing us to write setInterval(() => this.myMethod()) if we’re inside the myArray method.

If you need to support IE, use the Function.prototype.bind() method, which lets you specify the value that should be used as this for all calls to a given function. That lets you easily bypass problems where it’s unclear what this will be, depending on the context from which your function was called.

Usage notes

The setInterval() function is commonly used to set a delay for functions that are executed again and again, such as animations. You can cancel the interval using clearInterval() .

If you wish to have your function called once after the specified delay, use setTimeout() .

Delay restrictions

It’s possible for intervals to be nested; that is, the callback for setInterval() can in turn call setInterval() to start another interval running, even though the first one is still going. To mitigate the potential impact this can have on performance, once intervals are nested beyond five levels deep, the browser will automatically enforce a 4 ms minimum value for the interval. Attempts to specify a value less than 4 ms in deeply-nested calls to setInterval() will be pinned to 4 ms.

Browsers may enforce even more stringent minimum values for the interval under some circumstances, although these should not be common. Note also that the actual amount of time that elapses between calls to the callback may be longer than the given delay ; see Reasons for delays longer than specified for examples.

Ensure that execution duration is shorter than interval frequency

If there is a possibility that your logic could take longer to execute than the interval time, it is recommended that you recursively call a named function using setTimeout() . For example, if using setInterval() to poll a remote server every 5 seconds, network latency, an unresponsive server, and a host of other issues could prevent the request from completing in its allotted time. As such, you may find yourself with queued up XHR requests that won’t necessarily return in order.

In these cases, a recursive setTimeout() pattern is preferred:

(function loop()  setTimeout(() =>  // Your logic here loop(); >, delay); >)(); 

In the above snippet, a named function loop() is declared and is immediately executed. loop() is recursively called inside setTimeout() after the logic has completed executing. While this pattern does not guarantee execution on a fixed interval, it does guarantee that the previous interval has completed before recursing.

Specifications

Browser compatibility

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See also

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This page was last modified on Apr 8, 2023 by MDN contributors.

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JavaScript Timing Events

The window object allows execution of code at specified time intervals.

These time intervals are called timing events.

The two key methods to use with JavaScript are:

• setTimeout(function, milliseconds )
  Executes a function, after waiting a specified number of milliseconds.
• setInterval(function, milliseconds )
  Same as setTimeout(), but repeats the execution of the function continuously.

The setTimeout() and setInterval() are both methods of the HTML DOM Window object.

The setTimeout() Method

The window.setTimeout() method can be written without the window prefix.

The first parameter is a function to be executed.

The second parameter indicates the number of milliseconds before execution.

Example

Click a button. Wait 3 seconds, and the page will alert «Hello»:

How to Stop the Execution?

The clearTimeout() method stops the execution of the function specified in setTimeout().

The window.clearTimeout() method can be written without the window prefix.

The clearTimeout() method uses the variable returned from setTimeout() :

If the function has not already been executed, you can stop the execution by calling the clearTimeout() method:

Example

Same example as above, but with an added «Stop» button:

The setInterval() Method

The setInterval() method repeats a given function at every given time-interval.

The window.setInterval() method can be written without the window prefix.

The first parameter is the function to be executed.

The second parameter indicates the length of the time-interval between each execution.

This example executes a function called «myTimer» once every second (like a digital watch).

Example

function myTimer() const d = new Date();
document.getElementById(«demo»).innerHTML = d.toLocaleTimeString();
>

There are 1000 milliseconds in one second.

How to Stop the Execution?

The clearInterval() method stops the executions of the function specified in the setInterval() method.

The window.clearInterval() method can be written without the window prefix.

The clearInterval() method uses the variable returned from setInterval() :

Example

Same example as above, but we have added a «Stop time» button:

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