Javascript - 一切都超出范围

Question

所以，我有这段代码:

<script>

    //We'll pass you an array of two numbers. 
    //Return the sum of those two numbers plus the sum of all the numbers 
    //between them. 
    //The lowest number will not always come first.
    function sumAll(arr) {

        var number1 = arr[0];
        var number2 = arr[1];

        var lower_number;
        var bigger_number;


        if (number2 < number1) {
            number2 = lower_number;
            number1 = bigger_number;

        } else {
            number1 = lower_number;
            number2 = bigger_number;

        }
        var i;

        var something;

        for (i = lower_number; i < bigger_number; i++) {

            something = i + something;
            console.log(i);

        }
        return something;
    }
    sumAll([1, 4]);
    sumAll([4, 1]);

</script>

这行不通。当我尝试在控制台中查看结果(如 i 或 something)时，我只看到那里有 undefined。

有什么建议吗？

此外，我如何才能实际验证函数的结果？我是 JS 的新手。

谢谢。

Answer 1

console.log(i)正在显示 undefined因为那是变量的值。这不是范围问题。

您从未将任何内容分配给 lower_number .所以当你做 i = lower_number ，你在做i = undefined ，这就是记录的内容。

实际上，你永远不应该进入循环，因为i < bigger_number总是会失败，因为 i和 bigger_number都是undefined , 和 undefined < undefined是假的。

原因是你之前的赋值是倒过来的。本节:

    if (number2 < number1) {
        number2 = lower_number;
        number1 = bigger_number;
    } else {
        number1 = lower_number;
        number2 = bigger_number;
    }

应该是:

    if (number2 < number1) {
        lower_number = number2;
        bigger_number = number1;
    } else {
        lower_number = number1;
        bigger_number = number2;
    }

分配的顺序总是destination = source; (这对大多数编程语言都很常见)。

您可以通过记录函数调用来验证函数的结果:

console.log(sumAll([1, 4]));