Javascript 函数无法正常工作的问题(它将分数转换为小数)

Question

假设我有一个字符串(如分数)；

var num = "1/2";

为什么这有效:

var y = num.split(' ');
if (y.length > 1) {
    var z = y[1].split('/');
    var a = (+y[0] + (z[0] / z[1]));
    num = a;
} else {
    z = y[0].split('/');
    if (z.length > 1) {
        a = (z[0] / z[1]);
        num = a;
    }
}

alert(num); //The alert box shows my variable now as a decimal.

这不会:

function parseFractions(x) {
    var y = x.split(' ');
    if (y.length > 1) {
        var z = y[1].split('/');
        var a = (+y[0] + (z[0] / z[1]));
        x = a;
    } else {
        z = y[0].split('/');
        if (z.length > 1) {
            a = (z[0] / z[1]);
            x = a;
        }
    }
}

parseFractions(num); //Here I call my function.

alert(num);
//The alert box does not even show up. The fraction isn't converted into a decimal.

这基本上是相同的事情，唯一的区别是在第二个中我尝试将其变成一个函数，这样我就不必每次尝试将分数转换为小数时都重复这些代码行。

那我做错了什么？我想要通过函数实现的目标是否可行？感谢任何对此问题的了解!

Answer 1

num 的值没有更新，它不是通过引用传递的。

function parseFractions(x) {
    var y = x.split(' ');
    if (y.length > 1) {
        var z = y[1].split('/');
        var a = (+y[0] + (z[0] / z[1]));
        x = a;
    } else {
        z = y[0].split('/');
        if (z.length > 1) {
            a = (z[0] / z[1]);
            x = a;
        }
    }
    return x;
}

num = parseFractions(num);  //set num with the value return from the method
alert(num);