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    Understand the Difference Between for...in and for...of Loops in Javascript


    In general: Use for...in loops to loop over the keys of an object. Use for...of loops to iterate over an array or string.

    The two loop types: for...in and for...of behave differently in javascript. Both loops can be used with Arrays and Strings - but only for...of loops iterate over the values in order. for...in loops actually loop over the enumerable properties of an object. For an array, that means that a for...in loop iterates over the indices of the array - and order is not guaranteed. So use for...of for arrays or strings, and for...in for objects.