在js中，如果用for循环进行事件绑定，可能会遇到一点小问题，看下面第一个示例，无论点击哪个div，都会弹出3，即length。
因为这相当于事件绑定的同时，并没有把所对应的i进行一起绑定，i的值是最后一个值，即3。
示例1
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div {
width: 100px;
height: 100px;
background: red;
margin-bottom: 3px;
}
</style>
<script>
window.onload = function () {
var add_the_handlers = function (nodes) {
var i;
for (i = 0; i < nodes.length; i++) {
nodes[i].onclick = function (e) {
alert(i);
};
}
};
var divs = document.getElementsByTagName(‘div‘);
add_the_handlers(divs);
}
</script>
<body>
<div></div>
<div></div>
<div></div>
</body>
</html>
再看下面两个例子，通过事件绑定的同时，通过函数调用而不是函数定义进行i与事件的绑定。
示例2
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<style>
div {
width: 100px;
height: 100px;
background: red;
margin-bottom: 3px;
}
</style>
<script>
window.onload = function () {
var add_the_handlers = function (nodes) {
var helper = function (index) {
return function (e) {
alert(index);
};
};
var i;
for (i = 0; i < nodes.length; i++) {
nodes[i].onclick = helper(i);
}
};
var divs = document.getElementsByTagName(‘div‘);
add_the_handlers(divs);
}
</script>
<body>
<div></div>
<div></div>
<div></div>
</body>
</html>
示例3
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div {
width: 100px;
height: 100px;
background: red;
margin-bottom: 3px;
}
</style>
<script>
window.onload = function () {
var add_the_handlers = function (nodes) {
var i;
for (i = 0; i < nodes.length; i++) {
(function (i) {
nodes[i].onclick = function () {
alert(i);
};
})(i);
}
};
var divs = document.getElementsByTagName(‘div‘);
add_the_handlers(divs);
}
</script>
<body>
<div></div>
<div></div>
<div></div>
</body>
</html>
