带有回调函数的 Javascript 不起作用

Question

这是我的 javascript 程序，它应该在代码底部输出警报语句，但没有出现。这是为什么？

//function mean
function mean(values, callback) {
    var total = 0;
    for (var i = 0, max = values.length; i < max; i++) {
        if (typeof callback === "function") {
            total += callback(value[i]);
        } else {
            total += values[i];
        }
    }
}

var result = mean([2, 5, 7, 11, 4], function (x) {
    return 2 * x;
});

alert("The result mean is " + result + ".");

Answer 1

您需要返回total并将value更改为values。

function mean(values, callback) {
    var total = 0;
    for (var i = 0, max = values.length; i < max; i++) {
        if (typeof callback === "function") {
            total += callback(values[i]);
        } else {
            total += values[i];
        }
    }
    return total;
}

var result = mean([2, 5, 7, 11, 4], function (x) {
    return 2 * x;
});

alert("The result mean is " + result + ".");

您可以将代码重写为更紧凑的方式:

function mean(values, callback) {
    callback = callback || function (x) { return x; };
    return values.reduce(function (r, a) {
        return r + callback(a);
    }, 0);
}

var result = mean([2, 5, 7, 11, 4], function (x) {
    return 2 * x;
});

alert("The result mean is " + result + ".");