JavaScript settimeout () issues to be aware of when using closure features _javascript tips

SetTimeout is often used to delay execution of a function:

Copy Code code as follows:

settimeout (function () {
...
}, timeout);

Sometimes the settimeout (function...,0) is used for asynchronous processing, for example:

Copy Code code as follows:

function f () {
..//Get Ready
settimeout (function () {
.../Do Something
}, 0);

return ...;
}

function f is returned before the function processor set by settimeout.

Be especially careful when using asynchronous processing, especially when using closure features;

For example:

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for (var i = 0; i < i++) {
settimeout (function () {
Console.log (i);
}, 0);
}

For the first time to use this method of students, it is likely that the program will print 0 ... 9, the result is actually printing 10 10;
The problem is that when the loop completes, the function is executed, and I has become 10,console.log (i) using 10!

Add your purpose is to print 0 ... 9, you can use the function parameter to save the 0....9 (in fact, the closure) in a different way:

Copy Code code as follows:

for (var i = 0; i < i++) {
SetTimeout ((function (i) {
return function () {
Console.log (i);
}
}) (i), 0);
}