The for.in loop shouldn't be used for Array iteration. You can remove the initializer ( i = 0) in the head of the for-in loop. Synta圎rror: for-in loop head declarations may not have initializers This example throws a Synta圎rror: 'use strict' In strict mode, however, a Synta圎rror is thrown. In non-strict mode, this head declaration is silently ignored and behaves like |for (var i in obj)|. That is, a variable is declared and assigned a value | for (var i = 0 in obj)|. The head of a for.in loop contains an initializer expression. Synta圎rror: for-in loop variable declaration may not have an initializer.

Synta圎rror: for-in loop head declarations may not have initializers (Firefox) Message Synta圎rror: for-in loop head declarations cannot have an initializer (Edge) This is not allowed in for-of loops in strict mode.

The JavaScript strict mode-only exception 'for-in loop head declarations may not have initializers' occurs when the head of a for.in contains an initializer expression, such as | for (var i = 0 in obj)|.

For of loop javascript