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javascript - How does the callback function access the value under the current function?
大家讲道理
大家讲道理 2017-05-16 13:35:48
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I defined an array variable in the function, which contains 6 elements, and then called the callback function in the function. The value of the array variable cannot be accessed in the callback function, but the length attribute can be accessed. I feel very confused and don't know how to solve it.

for(var i=0;i

Book.getBookByISBN() is a function I defined in other modules

大家讲道理
大家讲道理

光阴似箭催人老，日月如移越少年。

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伊谢尔伦
伊谢尔伦2017-05-16 13:37:48 4 floor

Because

for (var i = 0; i<10; i++) { setTimeout(function(){console.log(i)}); } for (var i = 0; i<10; i++) { (function(i){ setTimeout(function(){console.log(i)}); })(i) }

So

for(var i=0;i
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    巴扎黑
    巴扎黑2017-05-16 13:37:48 3 floor

    Put bookARR[i] in callback

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      左手右手慢动作
      左手右手慢动作2017-05-16 13:37:48 2 floor

      The reason has been mentioned before. In fact, it is just to pass in bookArr[i] where you define the callback call in the Book.getBookByISBN() function. Understand the formal parameters and actual parameters

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        漂亮男人
        漂亮男人2017-05-16 13:37:48 1 floor

        This is a typical asynchronous problem, and the scope of i is still within it.
        Because I’m waiting for you asynchronouslygetBookByISBN方法调用callback的时候i=bookARR.length。这已经越界了,所以是undefined.

        Solution:
        1. Closure
        2.let

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