Simple application of JavaScript closure examples

This article mainly introduces the simple application of JavaScript closures in detail, which has certain reference value. Interested friends can refer to

closure definition

In JavaScript, when an inner function is referenced by a variable outside its outer function, a closure is formed. Simply put, a closure is a function that can read the internal variables of other functions.

The role of closure:

1. You can read the variables inside the function
2. Keep the values ​​of these variables in memory. .
Simple application of closure

Example 1:

function a() { 
  var i = 0; 
 function b() {
  console.log(++i);
 } 
 return b;
}      
var c = a();  //执行完var c=a()后，变量c指向了函数b，再执行c()后就会显示i的值(为1)。
c();    //输出1

Example 2:

(function() { 
var i = 0; 
 return function(){
   console.log(++i);
  }
})()();     //输出1

Example three:

##

(function(i) { 
 return function(){
   console.log(++i);
  }
})(0)();     //输出1

Example four:

##

for (var i = 0; i < 3; i++) {
 setTimeout((function(i) {    
  return function() {
   console.log(i);
  };
 })(i), 2000);
 console.log(i+10);
}      //输出 10 11 12 （隔两秒后）0 1 2

Example 5:

for (var i = 0; i < 3; i++) {
 setTimeout((function(i) {
  return function() {
   console.log(i);
  };
 })(i)(), 2000);
 console.log(i+10);
}      //立即输出 0 10 1 11 2 12 ，（两秒后运行程序结束）

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