The use of the In keyword in JS

Source: Internet
Author: User

1. In for ... In declares a loop/iterate operation for an array or an object's properties.
Example: var a = new Array;
For (x in a) {
Console.log (x);

2. Determine whether an object is an element/attribute of an array/object:
Format: (variable in object) ... Attention
When an "object" is an array, "variable" refers to the "index" of the arrays;
When "Object" is an object, "variable" refers to the object's "Properties".

PS: Special Note If the object is an array, the preceding variable refers to the index, not the value inside.

The use of the In keyword in JS

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