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This article is about how ES5 implements array map methods. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Implementation of Array map method with ES5

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It is worth mentioning that the second parameter of map is the this point in the first parameter callback. If the first parameter is an arrow function, setting the second this will fail because of the lexical binding of the arrow function.

In addition, the sparse array is processed, and the hasOwnProperty is used to determine whether the element of the current subscript exists in the array.

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