具有回调功能的Javascript无法正常工作

Question

Here is my javascript program and it supposed to output the alert statement at the bottom of the code but is not apppearing. Why is it?

//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

You need to return total and change value to 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 + "."); 

You can rewrite the code to a more compact way:

 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 + "."); 

Answer 2

以及Pointy提到的错别字，如果我没看错，您永远不会从均值中返回值，请尝试返回合计

Answer 3

您必须在回调函数中返回total，并确保没有将values变量键入为value。