For循环和变量

Question

var prompt1 = prompt("Number Here");
var something2 = prompt("Increment Here");
for (var i = 5; i <= prompt1; i += 5) {
    alert(i);
}

http://jsfiddle.net/davidhin/wte7d5k9/

为什么当我改变i += 5时i += something2,代码停止工作？

Answer 1

因为something2是String.用于for循环Number(something2)转换为Number.