Conditions that generate closures

The inner function can access the scope of the outer function.

function init() {
    var name = "Mozilla"; // Name is a local variable created by init
    function displayName() { // displayName() is an inner function, a closure
        alert(name); // Use a variable declared in the parent function
    }
    displayName();
}
init();// Console run result: Mozilla
//
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The role of closures

  1. Causes variables inside a function to remain in memory after the function completes execution (extends the life of local variables)
  2. A variable or function that enables an external function to operate on an internal function

` `

function foo(){
	var a=3;
	function b(){
		a++;
		console.log(a)
	}
	function c(){
		a--;
		console.log(a)
	}
	return c;
}
foo()();// console Execution result: 2

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The life cycle of closures

Generation of closures: Generation of internal nested function definitions after completion of execution.

Closure death: When internally nested functions become junk objects

Application of closures

  • A JS file with a specific function
  • Encapsulate all data and functionality inside functions that are private
  • Only one object or function containing n methods is exposed
  • The consumer of the module only needs to invoke the exposed object invocation method to implement the corresponding function

Method 1

// The following is the internal code of js file: mymodule.js
function muModule(){
/ / private
var msg='My atguigu'
funtion doSomething(){
  console.log('doSomething()'+msg.toUpperCase())
  //
 }
 funtion.doOtherthing(){
 console.log('doOtherthing() '+ msg.tolowerCase ())} return{doSomething: doSomething, doOtherthing: DoOtherthing}// expose only one object or function containing n methods}