Javascript闭包函数

Javascript Closure functions

本文关键字：函数 闭包 Javascript      更新时间：2023-09-26

所以我是javascript的新手，我正在寻找一种计算函数执行次数的方法。代码随机生成一个正方形或圆形，并从显示的形状显示到单击它时(reactionTime(。这很好用。但我正在寻找一种方法来跟踪形状被点击的次数，然后最终计算每次点击的平均时间。如果有帮助的话，我有很好的C++背景。

为了计算点击次数，我考虑添加一个闭包函数。从这里：我如何知道一个函数用javascript/jquery调用了多少次？

    myFunction = (function(){
        var count = 0;
        return function(){
            count++
            alert( "I have been called " + count + " times");
        }
     })();

从这里开始：函数计数调用

    var increment = function() {
        var i = 0;
        return function() { return i += 1; };
    };
    var ob = increment();

但我尝试了一个全局变量和几个闭包函数的变体，但都没有成功(请查看注释(。我试着把闭包函数放在其他函数中。我还尝试了一些类似的东西：

    var increment = makeBox();

我想知道是否有人能指引我走向正确的方向。非常感谢！

    var clickedTime; var createdTime; var reactionTime;
    var clicked; var avg = 0;
    avg = (avg + reactionTime) / clicked;
    document.getElementById("clicked").innerHTML = clicked;
    document.getElementById("avg").innerHTML = avg;
    function getRandomColor() {
    ....
    }
    function makeBox() { // This is the long function that makes box
        createdTime = Date.now();
        var time = Math.random();
        time = time * 3000;
        ///////// var increment = function () {
            var i = 0;
            //return function() { return i += 1; };
            i++;
            return i;
        ///////// };

        // clicked++; /////////// global variable returns NaN
        // console.log(clicked);
        // alert("Clicked: "+clicked);
        setTimeout(function() {
            if (Math.random() > 0.5) {
                document.getElementById("box").style.borderRadius="75px"; }
            else {
                document.getElementById("box").style.borderRadius="0px"; }
            var top = Math.random(); top = top * 300;
            var left = Math.random(); left = left * 500;
            document.getElementById("box").style.top = top+"px";
            document.getElementById("box").style.left = left+"px";
            document.getElementById("box").style.backgroundColor = getRandomColor();
            document.getElementById("box").style.display = "block";
            createdTime = Date.now();
        }, time);
    }
    ob = increment(); //////////////////////// I think this gives me 1 every time
    alert("Increment: "+ob); //////////////////
    document.getElementById("box").onclick = function() {
        clickedTime = Date.now();
        reactionTime= (clickedTime - createdTime)/1000;
        document.getElementById("time").innerHTML = reactionTime;
        this.style.display = "none";
        makeBox();
    }
    makeBox();

您有一些问题，但要回答您的问题：

  • 您没有将clicked定义为数字(或任何其他类型(，因此尝试对undefined执行操作会返回NaN。。。因为这不是一个数字
  • 您的第二次尝试var i = 0;将不起作用，因为在每个函数调用上都重新定义了i

只要将gobal变量clicked设置为零，就应该能够使用它。

下面是一个例子，展示了闭包如何计数对函数的调用：

function add5(y) {
    //A totally normal function
    return y + 5;
}
var counter = 0, /*a counter scoped outside of the function counter function*/
    trackedAdd5 = (function (func) {
        /*This anonymous function is incrementing a counter and then calling the function it is passed*/
        return function () {
            counter++;
            /*The trick is this function returns the output of calling the passed in function (not that it is applying it by passing in the arguments)*/
            return func.apply(this, arguments);
        }
    })(add5); /*calling this tracking function by passing the function to track*/
document.getElementById('run').addEventListener('click', function () {
    /*Here we are treating this new trackedAdd5 as a normal function*/
    var y = document.getElementById('y');
    y.value = trackedAdd5(parseInt(y.value, 10));
    /*Except the outer counter variable now represents the number of times this function has been called*/
    document.getElementById('counter').value = counter;
});
<label> <code>y = </code> 
    <input id='y' value='0' />
    <button id='run'>add5</button>
</label>
<br/>
<label><code>add5()</code> was called
    <input readonly id='counter' value='0' />times</label>

makeBox.click = 0; // define the function's counter outside the function
makeBox.click++; // replace the `i` usage with this inside the function

关于ob = increment();：使用错误(多次重新定义ob(；

var ob = increment(); // define it once
ob(); // increments the counter
// another way to define `increment`:
var increment = (function () {
    var i = 0;
    return function () {
        return i += 1;
    };
})();
ob = increment(); // ob becomes 1 initially
ob = increment(); // ob becomes 2, etc.
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