Introduction of JavaScript settimeout and setinterval timing mechanism

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ShowTime (); function ShowTime () { var today = new Date (); Alert ("The time is:" + today.tostring ()); SetTimeout ("ShowTime ()", 5000); }

Once this function is called, the time is displayed every 5 seconds.

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settimeout (function () { Alert (' Hello! '); }, 0); SetInterval (callbackfunction, 100);

It is assumed that the greeting method in settimeout is executed immediately, because it is not a figment of the imagination, but rather a JavaScript API document that explicitly defines how many milliseconds the second parameter meaning is, and the callback method is executed. This is set to 0 milliseconds, and is taken for granted immediately.
The same callbackfunction method for SetInterval is executed immediately at intervals of 100 milliseconds. Believe it!

But with the growing and enriching experience of JavaScript application development, one day you find a strange piece of code that you don't understand:

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Div.onclick = function () { settimeout (function () { document.getElementById (' Inputfield '). focus (); }, 0); };

Since it is 0 milliseconds to execute, then what else to do with settimeout, at the moment, the firm belief has begun to waver.

Until the very last day, you accidentally wrote a bad piece of code:

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settimeout (function () { while (true) { } }, 100); settimeout (function () { Alert (' Hello! '); }, 200); SetInterval (callbackfunction, 200);

The first line of code into the dead loop, but soon you will find that, second, the third line is not expected, alert greetings have not seen, Callbackfunction also heard!

If the timer function is not processed, then SetInterval will continue to execute the same code until the browser window closes, or the user moves to another page. However, there are ways to terminate the execution of the settimeout and setinterval functions.

When the setinterval call completes, it returns a timer ID that can be accessed by the timer in the future and, if passed to Clearinterval, terminates the execution of the invoked process code, as follows:

File:

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Settimeout_setinterval3.js (excerpt) var intervalprocess = setinterval ("alert (' goal! ')", 3000); var stopgoallink = document.getElementById ("Stopgoallink"); Attacheventlistener (Stopgoallink, "click", Stopgoal, false); function Stopgoal () { Clearinterval (intervalprocess); }

As long as click on the Stopgoallink, no matter when the click, Intervalprocess will be canceled, will not continue to carry out repeated intervalprocess. If SetTimeout is canceled within the timeout period, this termination effect can also be implemented on settimeout

Summary:

In fact, settimeout and setinterval have the same syntax. They all have two parameters, one is the code string that will be executed, and one is the time interval in milliseconds, and the code will be executed after that time period.

However, these two functions are different, setinterval after the execution of the code, after the fixed time interval, it will also automatically repeat the code, and settimeout only one time to execute the code.