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This article mainly introduces why vue do not use the for in loop to traverse the array, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

Do not use for in loops to traverse the array

You should all know that the for in loop is used to traverse objects, but can it be used to traverse arrays? The answer is yes, because an array is also an object in a sense, but there are some pitfalls if you use it to traverse the array: it traverses the properties on the array prototype chain.

Let arr = [1,2]; for (let key in arr) {console.log (ARR [key]); / will print 1,2} / / but if you add a method Array.prototype.test = function () {}; for (let key in arr) {console.log (ARR [key]) to the Array prototype chain, 1, 2, ARR () {} will be printed at this time

Because we cannot guarantee that the array prototype chain will not be manipulated in the project code, nor can we guarantee that the introduced third-party libraries will not operate on it, do not use the for in loop to traverse the array.

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