Several examples show how to run setTimeout in JS, jssettimeout

Several examples show how to run setTimeout in JS, jssettimeout

<Span style = "font-size: 18px;"> example: 1 </span>

Function test () {var a = 1; setTimeout (function () {alert (a); a = 5 ;}, 1000) ;}test (); alert (0 ); // The first two settimeouts are delayed. Therefore, execute this

Result: 0 is displayed, and 1 is displayed.

Example 2

function test() {  var a = 1;  setTimeout(function() {    alert(a);    a = 5;  }, 1000);  alert(a);}test();alert(0);

Result: 1 is displayed, 0 is displayed, and 1 is displayed.

Execute alert () in test () first, because the function is not executed yet, so a is still 1. because the function is still delayed, alert (0) is executed, and the last time is reached, alert (a) is executed. Because a has changed to 1, the last pop-up is 1.

Example: 3:

Function test () {var a = 1; setTimeout (function () {alert (a); a = 5 ;}, 1000); a = 19 ;}test (); alert (0); // The preceding alert is executed first because of the delay of setTimeout.

Result: 0 is displayed, and 19 is displayed.

Function (){
Alert ();
A = 5;
}

But a = 19 will still be executed as usual, instead of waiting until the delay ends. Therefore, when executing this delayed function, a = 19!

Example 4

Function test () {var a = 1; setTimeout (function () {alert (a); a = 5 ;}, 1000); a = 19; setTimeout (function () {alert (a); a = 4 ;}, 3000) ;}test (); alert (0); // The first two settimeouts are delayed.

Result: 0 is displayed, 19 is displayed, and 5 is displayed.

Additional explanations: global variables and local variables!

Global variables: defined outside the function, or assigned values in the function, but the var keyword is not added before, are global variables.

Local variables: variables defined within the function with the preceding var keyword

SetTimeOut usage in Js

SetTimeOut ("a ()", 1000)

There is a problem. Since you have all refreshed. Then how can the subsequent JavaScript code be executed?

I think it is impossible for you to refresh and then execute JS Code. If you implement it, paste it and learn it.

JS setTimeout Method Problems

When you click the mouse, test (time) transfers the global variable time = 60 to the function.
SetTimeout ("test ()", 1000); when the call is made again, no parameter is passed. Therefore, after the call is made again, num = 0 is terminated.

New_num = -- num; // equivalent to num = num-1; new_num = num;
Test (-- num) each time the value is uploaded, the previous value is reduced by 1.

New_num = num --; // equivalent to new_num = num; num = num-1;
Test (num --) does not change each value