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, arg1)
setInterval(func, delay, arg1, arg2)
setInterval(func, delay, arg1, arg2, argN)
Parameters
func
-
A function
to be executed every delay
milliseconds. The first execution happens after delay
milliseconds.
code
-
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.
-
delay
Optional
-
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.
-
arg1
, …,argN
Optional
-
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) {
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 World</h3>
</div>
<button id="start">Start</button>
<button id="stop">Stop</button>
CSS
.go {
color: green;
}
.stop {
color: red;
}
JavaScript
let nIntervId;
function changeColor() {
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);
nIntervId = null;
}
document.getElementById("start").addEventListener("click", changeColor);
document.getElementById("stop").addEventListener("click", stopTextColor);
Result
See also: clearInterval()
.
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();
myArray.myMethod(1);
setTimeout(myArray.myMethod, 1000);
setTimeout(myArray.myMethod, 1500, "1");
setTimeout.call(myArray, myArray.myMethod, 2000);
setTimeout.call(myArray, myArray.myMethod, 2500, 2);
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(() => {
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
|
Desktop |
Mobile |
|
Chrome |
Edge |
Firefox |
Internet Explorer |
Opera |
Safari |
WebView Android |
Chrome Android |
Firefox for Android |
Opera Android |
Safari on IOS |
Samsung Internet |
setInterval |
1 |
12 |
1 |
4 |
4 |
1 |
4.4 |
18 |
4 |
10.1 |
1 |
1.0 |
supports_parameters_for_callback |
1 |
12 |
1 |
10 |
≤15 |
1.2 |
≤37 |
18 |
4 |
≤14 |
1 |
1.0 |
worker_support |
3 |
12 |
3.5 |
10 |
≤12.1 |
4 |
4.4 |
18 |
4 |
≤12.1 |
5 |
1.0 |
See also