Introduction to JS closures

This article mainly introduces the introduction of JS closures, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

1. Scope

    var x = 0  //全局变量 x
    var y = 10 //全局变量 y
    var fun1 = function(){
        var x = 1  //fun1函数局部变量 x
        console.log(x++)
        console.log(y)
    } 
    fun1() //输出 1  10 函数内可以访问函数上级的变量
    console.log(x) //输出0 函数外部不能调用函数内部的局部变量

2. Closure

<!-- 闭包：有权访问另一个函数作用域中的变量的函数。大多是在一个函数内部创建另一个函数 -->
    var x = 0  //全局变量 x
    var fun1 = function(){
        var x = 1  //fun1函数局部变量 x
        function fun2() {
            console.log(x++) //当x = 1时 x++ = x ; ++x = x+1
        }
        return fun2  //此时fun2就是一个闭包
    } 
    var run1 = fun1()
    run1() //输出 1 
    run1() //输出 2 run1是函数是引用类型，上一步运行run1将变量x改变进而影响这步的输出

    var run2 = run1
    run2() //输出 3  因为run2 = run1 run1和run2是函数属于引用类型 所以共用一个作用域链
    run2() //输出 4

    var run3 = fun1()
    run3() //输出 1 这里不是5 run3有自己的作用域链
    run3() //输出 2

    console.log(x) //输出 0

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