SetTimeout () Usage

Source: Internet
Author: User
When setTimeout is executed, it executes expression 1 at a specified time after loading. Basic usage: run a piece of code: vari0; setTimeout (& quot; I + 1; alert (I) & quot;, 1000); execute a function: vari0; setTimeout (function () {I + 1; ale...


When setTimeout is executed, it executes expression 1 at a specified time after loading. Basic usage: run a piece of code: var I = 0; setTimeout ("I + = 1; alert (I) ", 1000); execute a function: var I = 0; setTimeout (function () {I + = 1; alert (I) ;}, 1000 );


Body: how to use setTimeout () in the js class

SetTimeout (expression, latency)

SetTimeout (expression, interaction time)

The delay time/interaction time is in the unit of luxury seconds (1000 ms = 1 s)

When setTimeout is executed, it is executed once after the specified delay after loading, and only once

When setTimeout is executed, it executes the expression once every specified time after loading.

1. Basic usage:

Run a piece of code:

Var I = 0;

SetTimeout ("I + = 1; alert (I)", 1000 );

Execute a function:

Var I = 0;

SetTimeout (function () {I + = 1; alert (I) ;}, 1000 );

// Compare the two methods above.

Next, let's execute another function:

Var I = 0;

Function test (){

I + = 1;

Alert (I );


SetTimeout ("test ()", 1000 );

You can also do this:

SetTimeout (test, 1000 );


The prototype of setTimeout is as follows:

ITimerID = window. setTimeout (vCode, iMilliSeconds [, sLanguage])

SetTimeout has two forms:

SetTimeout (code, interval)

SetTimeout (func, interval, args)

The code is a string.

Func is a function.

Note that the meaning of "function" is an expression rather than a statement.

For example, if you want to periodically execute a function

Function (){




SetTimeout ("a ()", 1000)


SetTimeout (a, 1000)

Note that the second form is a. Do not write it as a (). Remember !!!

Expand, no matter what you write here, if it is a variable, it must be a variable pointing to a function; if it is a function, then its return value is a function.

2. use setTimeout to implement the setInterval Function

The idea is simple, that is, calling a function without stopping the execution of itself is a bit like recursion.

Var I = 0;

Function xilou (){

I + = 1;

If (I> 10) {alert (I); return ;}

SetTimeout ("xilou ()", 1000 );

// You can also use this

// SetTimeout (xilou, 1000 );


3. use setTimeout in the class

Finally, the question is true. In fact, all the problems encountered in the class are about this. As long as this problem is solved, everything will be done.

Haha. Let's analyze:

Function xilou (){

This. name = "xilou ";

This. sex = "male ";

This. num = 0;


Xilou. prototype. count = function (){

This. num + = 1;

Alert (this. num );

If (this. num> 10) {return ;}

// Perform the test in four ways, one by one.

SetTimeout ("this. count ()", 1000); // A: an error occurs when calling x. count (): the object does not support this attribute or method.

SetTimeout ("count ()", 1000); // B: Error display: an object is missing

SetTimeout (count, 1000); // C: error message: 'Count' undefined

// The fourth type is shown below.

Var self = this;

SetTimeout (function () {self. count () ;}, 1000); // D: Correct


Var x = new xilou ();

X. count ();

Error analysis:

A: this actually refers to the window object, not the current instance object.

Count () and count in B: And C: actually refer to a separate function named count (), but it can also be window. count (), because window. count () can be omitted as count ()

D: Direct the variable self to the current instance object, so that the js parsing engine will not confuse who this refers.

Even though we know that this in setTimeout ("this. count ()", 1000) refers to the window object, we still don't understand why

Window object ^_^ (a little dizzy ...)

Then we can imagine how this setTimeout is defined:

SetTimeout is a window method. The full name is as follows: window. setTimeout ()

It should be defined as follows:

Window. setTimeout = function (vCode, iMilliSeconds [, sLanguage]) {

// ...... Code

Return timer // return a token


So when this is passed in to setTimeout (), of course it refers to the current Object window to which it belongs.

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