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var abc = ["A", "B", "C"];
for (var i in ABC) {
Console.log (i);
}

The output is 0, 1, 2 that is, the for (VAR i in ABC) I is the index of the array items in addition, the string entry in the array needs to be added "" But for the object: var ob = {
Name: "tt",
Age: "12"
};
for (var i in OB) {
Console.log (i);
The output is name and age. When you use the for-in loop, you return an enumerable property that can be accessed through an object, which includes both the attributes that exist in the instance and the properties that exist in the prototype. Although an array is also an object, be aware of the differences between arrays and objects

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