javascript loop array

	var arr = [1, 2, 3, 4, 5],
	len = arr.length;
	// Method1 (逆)
	while (len--) {
	console.log(arr[len]);
	}
	// Method2 (逆)
	for (var i = arr.length; i--;) {
	console.log(arr[i]);
	}
	// Method3 (順)
	for (var i = 0, a; a = arr[i++];) {
	console.log(a);
	}
	// Method4 (順)
	var el;
	while (el = arr.shift()) {
	console.log(el);
	}

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