Repeatedly calls a function or executes a code snippet, with a fixed time delay between each call. Returns an intervalID.

Syntax

var intervalID = window.setInterval(func, delay[, param1, param2, ...]);
var intervalID = window.setInterval(code, delay);
  • intervalID is a unique interval ID you can pass to clearInterval().
  • func is the function you want to be called repeatedly.
  • code, in the alternate syntax, is the string of code you want to be executed repeatedly.  (This syntax is not recommended for the same reasons that using eval() should be avoided.)
  • delay is the number of milliseconds (thousandths of a second) that the setInterval() function should wait before each call to func. As with setTimeout, there is a minimum delay enforced.
  • param1, param2, and so forth, are additional parameters that are passed through to the function specified by func.

Passing additional parameters to the function in the first syntax does not work in Internet Explorer 9 and earlier. To enable this functionality on that browser, use a polyfill (see the Callback arguments section).

Note: Prior to Gecko 13 (Firefox 13.0 / Thunderbird 13.0 / SeaMonkey 2.10), Gecko passed an extra parameter to the callback routine, indicating the "actual lateness" of the timeout in milliseconds. This non-standard parameter is no longer provided.
Note: Extension code should use this method with care because the Window object might be updated when Firefox is checking for extension updates; this can then cause timers to be lost. In such case, you'll find that the nsITimer interface can provide more reliable results.

Examples

Example 1: Basic syntax

The following example demonstrates the basic syntax of the function.

var intervalID = window.setInterval(myCallback, 500);

function myCallback() {
  // Your code here
}

Example 2: Alternating two colors

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

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <title>setInterval/clearInterval example</title>

  <script>
    var nIntervId;
 
    function changeColor() {
      nIntervId = setInterval(flashText, 1000);
    }
 
    function flashText() {
      var oElem = document.getElementById("my_box");
      oElem.style.color = oElem.style.color == "red" ? "blue" : "red";
    }
 
    function stopTextColor() {
      clearInterval(nIntervId);
    }
  </script>
</head>
 
<body onload="changeColor();">
  <div id="my_box">
    <p>Hello World</p>
  </div>

  <button onclick="stopTextColor();">Stop</button>
</body>
</html>

Example 3: Typewriter simulation

The following example simulates typewriter by first clearing and then slowly typing content into the NodeList that matches a specified group of selectors.

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>JavaScript Typewriter - MDN Example</title>
<script>
  function Typewriter (sSelector, nRate) {

  function clean () {
    clearInterval(nIntervId);
    bTyping = false;
    bStart = true;
    oCurrent = null;
    aSheets.length = nIdx = 0;
  }

  function scroll (oSheet, nPos, bEraseAndStop) {
    if (!oSheet.hasOwnProperty("parts") || aMap.length < nPos) { return true; }

    var oRel, bExit = false;

    if (aMap.length === nPos) { aMap.push(0); }

    while (aMap[nPos] < oSheet.parts.length) {
      oRel = oSheet.parts[aMap[nPos]];

      scroll(oRel, nPos + 1, bEraseAndStop) ? aMap[nPos]++ : bExit = true;

      if (bEraseAndStop && (oRel.ref.nodeType - 1 | 1) === 3 && oRel.ref.nodeValue) {
        bExit = true;
        oCurrent = oRel.ref;
        sPart = oCurrent.nodeValue;
        oCurrent.nodeValue = "";
      }

      oSheet.ref.appendChild(oRel.ref);
      if (bExit) { return false; }
    }

    aMap.length--;
    return true;
  }

  function typewrite () {
    if (sPart.length === 0 && scroll(aSheets[nIdx], 0, true) && nIdx++ === aSheets.length - 1) { clean(); return; }

    oCurrent.nodeValue += sPart.charAt(0);
    sPart = sPart.slice(1);
  }

  function Sheet (oNode) {
    this.ref = oNode;
    if (!oNode.hasChildNodes()) { return; }
    this.parts = Array.prototype.slice.call(oNode.childNodes);

    for (var nChild = 0; nChild < this.parts.length; nChild++) {
      oNode.removeChild(this.parts[nChild]);
      this.parts[nChild] = new Sheet(this.parts[nChild]);
    }
  }

  var
    nIntervId, oCurrent = null, bTyping = false, bStart = true,
    nIdx = 0, sPart = "", aSheets = [], aMap = [];

  this.rate = nRate || 100;
 
  this.play = function () {
    if (bTyping) { return; }
    if (bStart) {
      var aItems = document.querySelectorAll(sSelector);

      if (aItems.length === 0) { return; }
      for (var nItem = 0; nItem < aItems.length; nItem++) {
        aSheets.push(new Sheet(aItems[nItem]));
        /* Uncomment the following line if you have previously hidden your elements via CSS: */
        // aItems[nItem].style.visibility = "visible";
      }

      bStart = false;
    }

    nIntervId = setInterval(typewrite, this.rate);
    bTyping = true;
  };
 
  this.pause = function () {
    clearInterval(nIntervId);
    bTyping = false;
  };
 
  this.terminate = function () {
    oCurrent.nodeValue += sPart;
    sPart = "";
    for (nIdx; nIdx < aSheets.length; scroll(aSheets[nIdx++], 0, false));
    clean();
  };
}
 
/* usage: */
var oTWExample1 = new Typewriter(/* elements: */ "#article, h1, #info, #copyleft", /* frame rate (optional): */ 15);
 
/* default frame rate is 100: */
var oTWExample2 = new Typewriter("#controls");

/* you can also change the frame rate value modifying the "rate" property; for example: */
// oTWExample2.rate = 150;
 
onload = function () {
  oTWExample1.play();
  oTWExample2.play();
};
</script>
<style type="text/css">
span.intLink, a, a:visited {
  cursor: pointer;
  color: #000000;
  text-decoration: underline;
}
 
#info {
  width: 180px;
  height: 150px;
  float: right;
  background-color: #eeeeff;
  padding: 4px;
  overflow: auto;
  font-size: 12px;
  margin: 4px;
  border-radius: 5px;
  /* visibility: hidden; */
}
</style>
</head>
 
<body>

<p id="copyleft" style="font-style: italic; font-size: 12px; text-align: center;">CopyLeft 2012 by <a href="https://developer.mozilla.org/" target="_blank">Mozilla Developer Network</a></p>
<p id="controls" style="text-align: center;">[&nbsp;<span class="intLink" onclick="oTWExample1.play();">Play</span> | <span class="intLink" onclick="oTWExample1.pause();">Pause</span> | <span class="intLink" onclick="oTWExample1.terminate();">Terminate</span>&nbsp;]</p>
<div id="info">
Vivamus blandit massa ut metus mattis in fringilla lectus imperdiet. Proin ac ante a felis ornare vehicula. Fusce pellentesque lacus vitae eros convallis ut mollis magna pellentesque. Pellentesque placerat enim at lacus ultricies vitae facilisis nisi fringilla. In tincidunt tincidunt tincidunt.
</div>
<h1>JavaScript Typewriter</h1>
 
<div id="article">
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam ultrices dolor ac dolor imperdiet ullamcorper. Suspendisse quam libero, luctus auctor mollis sed, malesuada condimentum magna. Quisque in ante tellus, in placerat est. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Donec a mi magna, quis mattis dolor. Etiam sit amet ligula quis urna auctor imperdiet nec faucibus ante. Mauris vel consectetur dolor. Nunc eget elit eget velit pulvinar fringilla consectetur aliquam purus. Curabitur convallis, justo posuere porta egestas, velit erat ornare tortor, non viverra justo diam eget arcu. Phasellus adipiscing fermentum nibh ac commodo. Nam turpis nunc, suscipit a hendrerit vitae, volutpat non ipsum.</p>
<form>
<p>Phasellus ac nisl lorem: <input type="text" /><br />
<textarea style="width: 400px; height: 200px;">Nullam commodo suscipit lacus non aliquet. Phasellus ac nisl lorem, sed facilisis ligula. Nam cursus lobortis placerat. Sed dui nisi, elementum eu sodales ac, placerat sit amet mauris. Pellentesque dapibus tellus ut ipsum aliquam eu auctor dui vehicula. Quisque ultrices laoreet erat, at ultrices tortor sodales non. Sed venenatis luctus magna, ultricies ultricies nunc fringilla eget. Praesent scelerisque urna vitae nibh tristique varius consequat neque luctus. Integer ornare, erat a porta tempus, velit justo fermentum elit, a fermentum metus nisi eu ipsum. Vivamus eget augue vel dui viverra adipiscing congue ut massa. Praesent vitae eros erat, pulvinar laoreet magna. Maecenas vestibulum mollis nunc in posuere. Pellentesque sit amet metus a turpis lobortis tempor eu vel tortor. Cras sodales eleifend interdum.</textarea></p>
<p><input type="submit" value="Send" />
</form>
<p>Duis lobortis sapien quis nisl luctus porttitor. In tempor semper libero, eu tincidunt dolor eleifend sit amet. Ut nec velit in dolor tincidunt rhoncus non non diam. Morbi auctor ornare orci, non euismod felis gravida nec. Curabitur elementum nisi a eros rutrum nec blandit diam placerat. Aenean tincidunt risus ut nisi consectetur cursus. Ut vitae quam elit. Donec dignissim est in quam tempor consequat. Aliquam aliquam diam non felis convallis suscipit. Nulla facilisi. Donec lacus risus, dignissim et fringilla et, egestas vel eros. Duis malesuada accumsan dui, at fringilla mauris bibStartum quis. Cras adipiscing ultricies fermentum. Praesent bibStartum condimentum feugiat.</p>
<p>Nam faucibus, ligula eu fringilla pulvinar, lectus tellus iaculis nunc, vitae scelerisque metus leo non metus. Proin mattis lobortis lobortis. Quisque accumsan faucibus erat, vel varius tortor ultricies ac. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed nec libero nunc. Nullam tortor nunc, elementum a consectetur et, ultrices eu orci. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque a nisl eu sem vehicula egestas.</p>
</div>
</body>
</html>

View this demo in action. See also: clearInterval().

Callback arguments

As previously discussed, Internet Explorer versions 9 and below do not support the passing of arguments to the callback function in either setTimeout() or setInterval(). The following IE-specific code demonstrates a method for overcoming this limitation.  To use, simply add the following code to the top of your script.

/*\
|*|
|*|  IE-specific polyfill that enables the passage of arbitrary arguments to the
|*|  callback functions of javascript timers (HTML5 standard syntax).
|*|
|*|  https://developer.mozilla.org/en-US/docs/Web/API/window.setInterval
|*|
|*|  Syntax:
|*|  var timeoutID = window.setTimeout(func, delay, [param1, param2, ...]);
|*|  var timeoutID = window.setTimeout(code, delay);
|*|  var intervalID = window.setInterval(func, delay[, param1, param2, ...]);
|*|  var intervalID = window.setInterval(code, delay);
|*|
\*/

if (document.all && !window.setTimeout.isPolyfill) {
  var __nativeST__ = window.setTimeout;
  window.setTimeout = function (vCallback, nDelay /*, argumentToPass1, argumentToPass2, etc. */) {
    var aArgs = Array.prototype.slice.call(arguments, 2);
    return __nativeST__(vCallback instanceof Function ? function () {
      vCallback.apply(null, aArgs);
    } : vCallback, nDelay);
  };
  window.setTimeout.isPolyfill = true;
}

if (document.all && !window.setInterval.isPolyfill) {
  var __nativeSI__ = window.setInterval;
  window.setInterval = function (vCallback, nDelay /*, argumentToPass1, argumentToPass2, etc. */) {
    var aArgs = Array.prototype.slice.call(arguments, 2);
    return __nativeSI__(vCallback instanceof Function ? function () {
      vCallback.apply(null, aArgs);
    } : vCallback, nDelay);
  };
  window.setInterval.isPolyfill = true;
}

Another possibility is to use an anonymous function to call your callback, although this solution is a bit more expensive. Example:

var intervalID = setInterval(function() { myFunc("one", "two", "three"); }, 1000);

Another possibility is to use function's bind. Example:

var intervalID = setInterval(function(arg1) {}.bind(undefined, 10), 1000);

Inactive tabs

(Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2)

Starting in Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), intervals are clamped to fire no more often than once per second in inactive tabs.

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):

myArray = ["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
// let's try to pass the 'this' 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.

A possible solution

A possible way to solve the "this" problem is to replace the two native setTimeout() or setInterval() global functions with two non-native ones that enable their invocation through the Function.prototype.call method. The following example shows a possible replacement:

// Enable the passage of the 'this' object through the JavaScript timers

var __nativeST__ = window.setTimeout, __nativeSI__ = window.setInterval;

window.setTimeout = function (vCallback, nDelay /*, argumentToPass1, argumentToPass2, etc. */) {
  var oThis = this, aArgs = Array.prototype.slice.call(arguments, 2);
  return __nativeST__(vCallback instanceof Function ? function () {
    vCallback.apply(oThis, aArgs);
  } : vCallback, nDelay);
};

window.setInterval = function (vCallback, nDelay /*, argumentToPass1, argumentToPass2, etc. */) {
  var oThis = this, aArgs = Array.prototype.slice.call(arguments, 2);
  return __nativeSI__(vCallback instanceof Function ? function () {
    vCallback.apply(oThis, aArgs);
  } : vCallback, nDelay);
};
Note: These two replacements also enable the HTML5 standard passage of arbitrary arguments to the callback functions of timers in IE. So they can be used as non-standard-compliant polyfills also. See the callback arguments paragraph for a standard-compliant polyfill.

New feature test:

myArray = ["zero", "one", "two"];

myArray.myMethod = function (sProperty) {
    alert(arguments.length > 0 ? this[sProperty] : this);
};

setTimeout(alert, 1500, "Hello world!"); // the standard use of setTimeout and setInterval is preserved, but...
setTimeout.call(myArray, myArray.myMethod, 2000); // prints "zero,one,two" after 2 seconds
setTimeout.call(myArray, myArray.myMethod, 2500, 2); // prints "two" after 2,5 seconds

Another, more complex, solution for the this problem is the following framework.

Note: JavaScript 1.8.5 introduces the Function.prototype.bind() method, which lets you specify the value that should be used as this for all calls to a given function. This lets you easily bypass problems where it's unclear what this will be, depending on the context from which your function was called.

MiniDaemon - A framework for managing timers

In pages requiring many timers, it can often be difficult to keep track of all of the running timer events. One approach to solving this problem is to store information about the state of a timer in an object. Following is a minimal example of such an abstraction. The constructor architecture explicitly avoids the use of closures. It also offers an alternative way to pass the this object to the callback function (see The "this" problem for details).

Note: For a more complex but still modular version of it (Daemon) see JavaScript Daemons Management. This more complex version is nothing but a big and scalable collection of methods for the Daemon constructor. However, the Daemon constructor itself is nothing but a clone of MiniDaemon with an added support for init and onstart functions declarable during the instantiation of the daemon. So the MiniDaemon framework remains the recommended way for simple animations, because Daemon without its collection of methods is essentially a clone of it.

minidaemon.js

/*\
|*|
|*|  :: MiniDaemon ::
|*|
|*|  Revision #2 - September 26, 2014
|*|
|*|  https://developer.mozilla.org/en-US/docs/Web/API/window.setInterval
|*|  https://developer.mozilla.org/User:fusionchess
|*|
|*|  This framework is released under the GNU Lesser General Public License, version 3 or later.
|*|  http://www.gnu.org/licenses/lgpl-3.0.html
|*|
\*/
 
function MiniDaemon (oOwner, fTask, nRate, nLen) {
  if (!(this && this instanceof MiniDaemon)) { return; }
  if (arguments.length < 2) { throw new TypeError("MiniDaemon - not enough arguments"); }
  if (oOwner) { this.owner = oOwner; }
  this.task = fTask;
  if (isFinite(nRate) && nRate > 0) { this.rate = Math.floor(nRate); }
  if (nLen > 0) { this.length = Math.floor(nLen); }
}
 
MiniDaemon.prototype.owner = null;
MiniDaemon.prototype.task = null;
MiniDaemon.prototype.rate = 100;
MiniDaemon.prototype.length = Infinity;
 
  /* These properties should be read-only */
 
MiniDaemon.prototype.SESSION = -1;
MiniDaemon.prototype.INDEX = 0;
MiniDaemon.prototype.PAUSED = true;
MiniDaemon.prototype.BACKW = true;
 
  /* Global methods */
 
MiniDaemon.forceCall = function (oDmn) {
  oDmn.INDEX += oDmn.BACKW ? -1 : 1;
  if (oDmn.task.call(oDmn.owner, oDmn.INDEX, oDmn.length, oDmn.BACKW) === false || oDmn.isAtEnd()) { oDmn.pause(); return false; }
  return true;
};
 
  /* Instances methods */
 
MiniDaemon.prototype.isAtEnd = function () {
  return this.BACKW ? isFinite(this.length) && this.INDEX < 1 : this.INDEX + 1 > this.length;
};
 
MiniDaemon.prototype.synchronize = function () {
  if (this.PAUSED) { return; }
  clearInterval(this.SESSION);
  this.SESSION = setInterval(MiniDaemon.forceCall, this.rate, this);
};
 
MiniDaemon.prototype.pause = function () {
  clearInterval(this.SESSION);
  this.PAUSED = true;
};
 
MiniDaemon.prototype.start = function (bReverse) {
  var bBackw = Boolean(bReverse);
  if (this.BACKW === bBackw && (this.isAtEnd() || !this.PAUSED)) { return; }
  this.BACKW = bBackw;
  this.PAUSED = false;
  this.synchronize();
};
Note: MiniDaemon passes arguments to the callback function. If you want to work on it with browsers that natively do not support this feature, use one of the methods proposed above.

Syntax

var myDaemon = new MiniDaemon(thisObject, callback[, rate[, length]]);

Description

Returns a JavaScript Object containing all information needed by an animation (like the this object, the callback function, the length, the frame-rate).

Parameters

thisObject
The this object on which the callback function is called. It can be an object or null.
callback
The function that is repeatedly invoked . It is called with three parameters: index (the iterative index of each invocation), length (the number of total invocations assigned to the daemon - finite or Infinity) and backwards (a boolean expressing whether the index is increasing or decreasing). It is something like callback.call(thisObject, index, length, backwards). If the callback function returns a false value the daemon is paused.
rate (optional)
The time lapse (in number of milliseconds) between each invocation. The default value is 100.
length (optional)
The total number of invocations. It can be a positive integer or Infinity. The default value is Infinity.

MiniDaemon instances properties

myDaemon.owner
The this object on which is executed the daemon (read/write). It can be an object or null.
myDaemon.task
The function that is repeatedly invoked (read/write). It is called with three arguments: index (the iterative index of each invocation), length (the number of total invocations assigned to the daemon - finite or Infinity) and backwards (a boolean expressing whether the index is decreasing or not) – see above. If the myDaemon.task function returns a false value the daemon is paused.
myDaemon.rate
The time lapse (in number of milliseconds) between each invocation (read/write).
myDaemon.length
The total number of invocations. It can be a positive integer or Infinity (read/write).

MiniDaemon instances methods

myDaemon.isAtEnd()
Returns a boolean expressing whether the daemon is at the start/end position or not.
myDaemon.synchronize()
Synchronize the timer of a started daemon with the time of its invocation.
myDaemon.pause()
Pauses the daemon.
myDaemon.start([reverse])
Starts the daemon forward (index of each invocation increasing) or backwards (index decreasing).

MiniDaemon global object methods

MiniDaemon.forceCall(minidaemon)
Forces a single callback to the minidaemon.task function regardless of the fact that the end has been reached or not. In any case the internal INDEX property is increased/decreased (depending on the actual direction of the process).

Example usage

Your HTML page:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <title>MiniDaemin Example - MDN</title>
  <script type="text/javascript" src="minidaemon.js"></script>
  <style type="text/css">
    #sample_div {
      visibility: hidden;
    }
  </style>
</head>

<body>
  <p>
    <input type="button" onclick="fadeInOut.start(false /* optional */);" value="fade in" />
    <input type="button" onclick="fadeInOut.start(true);" value="fade out">
    <input type="button" onclick="fadeInOut.pause();" value="pause" />
  </p>

  <div id="sample_div">Some text here</div>

  <script type="text/javascript">
    function opacity (nIndex, nLength, bBackwards) {
      this.style.opacity = nIndex / nLength;
      if (bBackwards ? nIndex === 0 : nIndex === 1) {
        this.style.visibility = bBackwards ? "hidden" : "visible";
      }
    }

    var fadeInOut = new MiniDaemon(document.getElementById("sample_div"), opacity, 300, 8);
  </script>
</body>
</html>

View this example in action

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 window.clearInterval().

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

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 window.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(function() {
      // 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

Specification Status Comment
WHATWG HTML Living Standard
The definition of 'WindowTimers.setInterval()' in that specification.		 Living Standard Initial definition (DOM Level 0)

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 1.0 1.0 (1.7 or earlier) 4.0 4.0 1.0
Supports parameters for callback[1] (Yes) (Yes) 10.0 (Yes) ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 1.0 1.0 1.0 (1) 6.0 6.0 1.0
Supports parameters for callback[1] ? ? ? ? ? ?

[1] Whether it supports the optional parameters when in its first form or not.

See also

Document Tags and Contributors

Tags: 
 Contributors to this page: Jorge.villalobos, maybe, rolfedh, bmwolfington, dreamweiver, Sebastianz, Sheppy, dyagmin, jeff_mangus, teoli, fusionchess, kertof, DDERRSS, jonathansampson, iamanupmenon, ethertank, m_gol, dancrumb, brunoais, BrianDiPalma, McGurk, wooptoo, jjoemb, Jesse, HarrisonM, ehynds, Nickolay, aeon, Ceth, 1212jtraceur, Mgjbot, Jabez, BenoitL, Dria, JesseW
 Last updated by: Jorge.villalobos,