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javascript - Solve js problem. Why is the result 5? Analyze it

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<title>Document</title>
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    <script>
     var test=(function(a){
          this.a=a;
          return function(b){
           return this.a+b;
          }
     }(function(a,b){
          return a;
          debugger;
     }(1,2))); 

     console.log(test(4))

     //结果是输出5 求解?

    </script>

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扔个三星炸死你扔个三星炸死你2661 days ago1026

reply all(3)I'll reply

  • 女神的闺蜜爱上我

    女神的闺蜜爱上我2017-07-07 10:36:36

    Memory

    let functionA = function (a) {
    this.a = a
    return function (b) {
        return this.a + b
    }
}

let argA = function (a, b) {
    return a
    debugger
}(1, 2)
// 实际上 argA 就等于 1，** 这个地方的 b 没有被用到 **

    The original formula is simplified to:

    let test = functionA(argA)

    After this sentence is executed, test is actually 

    function (b) {
    return this.a + b
}
// ** 这是一个带一个参数的函数，执行 test(4) 时 b 就是 4 **

    And at this time this.a is equal to 1. Therefore the result of test(4) is 5

    reply
    0
  • 黄舟

    黄舟2017-07-07 10:36:36

    Obviously it’s 5

      var test = function(a){
      this.a = a;
      return function(b){
        return this.a + b;
      }
    }(function(a,b){
      return a;
      }(1,2))

    Breakdown

        var test = function(a){
      this.a = a;
      return function(b){
        return this.a + b;
      }
    }
    
    var getA = function(a,b){
      return a;
    }
    
    test(getA(1,2))(4);

    If you still don’t understand this, you have to learn the basics

    reply
    0
  • typecho

    typecho2017-07-07 10:36:36

    First we need to understand the variable test. Test is actually a function, as follows

    var test = function(b){
    return this.a + b;
}

    The outer part is a function that is executed immediately. First, 

    function(a,b){
      return a;
 }(1,2)

    The result of this part is 1, that is to say, the code can be simplified to: 

    var test=(function(a){
      this.a=a;
      return function(b){
          return this.a+b;
      }
 }(1));

    In the above code, a=1, therefore, in test(4), we get: 

    var test=(function(a){ // a = 1
      this.a=a;
      return function(b){ // b = 4
          return this.a+b; // 得到 1 + 4
      }
 }(1));

    reply
    0
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