javascript - 简单例子中callback的使用值(value)

Question

以下示例演示回调:

示例 1: - 使用回调

<script>
// The callback method
function meaningOfLife() {
    console.log("The meaning of life is: 42");
}

// A method which accepts a callback method as an argument
function printANumber(number, callback) {
    console.log("The number you provided is: " + number);
    callback();
}

// Driver method
printANumber(6, meaningOfLife);
</script> 

结果:

The number you provided is: 6
The meaning of life is: 42

示例 2: - 普通函数调用

<script>
// A simple function
function meaningOfLife() {
    console.log("The meaning of life is: 42");
}

// Another simple function
function printANumber(number) {
    console.log("The number you provided is: " + number);
    meaningOfLife();
}

// Call to second function
printANumber(6);
</script> 

结果:

The number you provided is: 6
The meaning of life is: 42

Now, when I can get my result simply by normal function calling, then what is the use case of Callback? Why so much fuss? Even by making a simple call to a method from inside another function I can achieve my task (Always). Why in world then huge fuss of callback is there? What special work has it done in this example?

Answer 1

Why in world then huge fuss of callback is there?

因为调用者决定接下来应该调用什么。