A few examples to figure out how JS's settimeout works

<span style= "FONT-SIZE:18PX;" > Example:1</span>

function test () {  var a = 1;  SetTimeout (function () {    alert (a);    A = 5;  }, 1000);} Test (); alert (0);//The two settimeout in front of it is delayed so perform this first

Result: Pop 0 first, then pop up 1.

Example 2

function test () {  var a = 1;  SetTimeout (function () {    alert (a);    A = 5;  }, +);  alert (a);} Test (); alert (0);

Result: pops up 1 First, then pops 0, and finally pops up 1.

The alert () in test () is executed first because the function is not executed at this time, so a is still 1. Because the function is delayed, the alert (0) is executed, and the last time, the alert (a) is executed, because the previous a has become 1, so , and the last popup is 1.

Example: 3:

function test () {  var a = 1;  SetTimeout (function () {    alert (a);    A = 5;  }, +);  A = 19;} Test (); alert (0);//The preceding alert is executed first because the settimeout is delayed.

Result: 0 will pop up first, then pop up.

Deferred function () {
alert (a);
A = 5;
}

But the a=19 will still execute, not wait until the end of the delay. So, when executing this delayed function, a=19!

Example 4

function test () {  var a = 1;  SetTimeout (function () {    alert (a);    A = 5;  }, +);  A = 19;settimeout (function () {   alert (a);    A = 4;  }, 3000);} Test (); alert (0);//The two settimeout in front of it is delayed so perform this first

Result: Will pop up 0 first, then pop up 19, and finally pop up 5.

Additional explanations for global variables and local variables!

Global variables: Defined outside a function, or assigned within a function but not preceded by the VAR keyword, are global variables

Local variables: variables defined within a function and preceded by a var keyword

A few examples to figure out how JS's settimeout works