遇到一个关于 JavaScript 的 for 循环问题

function $(selector) {
    var str = selector.split(' '),
        temp,
        element = document;
    console.log(str[0]);
    for (var i = 0; i < str.length; i++) {//ID
        if (str[i].indexOf('#') === 0) {
            temp = str[i].replace('#', '');
            element = element.getElementById(temp);
        }
        else if (str[i].indexOf('.') === 0) {//Class
            temp = str[i].replace('.', '');
            element = element.getElementsByClassName(temp)[0];
        }
        else if (str[i].indexOf('#') === -1 && str[i].indexOf('.') === -1 && str[i].indexOf('[') === -1) {//Tag
            element = element.getElementsByTagName(str[i])[0];
        }
        else if (str[i].indexOf('[') === 0 && str[i].indexOf('=') === -1) {//属性
            temp = str[i].replace('[', '').replace(']', '');
            //console.log(temp)
            //console.log(element.length,element)
            //console.log(doc.length)
            for (var element = element.getElementsByTagName('*'), j = 0; j < element.length; j++) {
                if (element[j].hasAttribute(temp) === true) {
                    element = element[j];
                }
            }
        }
        else {//属性值
            temp = str[i].replace('[', '').replace(']', '');
            temp = temp.split('=');
            element = element.getElementsByTagName('*');
            for (var j = 0, l = element.length - 1; j < l; j++) {
                console.log('j=' + j, 'element.length=' + l);
                if (element[j].attributes.length != 0) {
                    //var xxx = element[j].attributes.length - 1;
                    console.log('j=' + j);
                    //for (var i = 0; i < xxx; i++) {
                    console.log('j=' + j);
                    if (console.log(j) && [j].attributes[temp[0]] != undefined && element[j].attributes[temp[0]].value === temp[1]) {
                        console.log('j=' + j);
                        element = element[j];
                    }
                    //}
                }

            }
        }
    }
    return element;
}

HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<div id="main" class="main2">
    <h1 id="tit" class="title">JavaScript</h1>
<!--comment-->
    <p class="test test1 test2">
        <span>
            <a href="baidu.com" class="baidu"></a>
            <a href="github.com" class="github"></a>
        </span>
    </p>
</div>
<div id="main2">
        <span>
            <a href="baidu.com" class="baidu">WEB</a>
            <a href="github.com" class="github">web</a>
        </span>
</div>
<ol></ol>
<script src="util.js"></script>
</body>
</html>

element

str

temp

console

11 条回复 • 2015-11-11 17:06:34 +08:00

domty

2015-11-10 18:07:02 +08:00

没细看,说错了当我没说
难道不是 j=4,l=4 的时候中止循环
所以 j=3 还在执行 j=4 不执行有错?

isbase

2015-11-10 18:09:36 +08:00

在 chrome 控制台执行 $('#main [class=github]') 后正确结果应该是返回
<a href="baidu.com" class="baidu"></a>

learnshare

2015-11-10 18:09:46 +08:00

没错啊，你自己这么写的

isbase

2015-11-10 18:12:02 +08:00

@domty 在 chrome 控制台查看日志 j 就没有循环到 4 ，到 3 就停止了

isbase

2015-11-10 18:17:15 +08:00

```
function $(selector) {
var str = selector.split(' '),
temp,
element = document;
console.log(str[0]);
for (var i = 0; i < str.length; i++) {//ID
if (str[i].indexOf('#') === 0) {
temp = str[i].replace('#', '');
element = element.getElementById(temp);
}
else if (str[i].indexOf('.') === 0) {//Class
temp = str[i].replace('.', '');
element = element.getElementsByClassName(temp)[0];
}
else if (str[i].indexOf('#') === -1 && str[i].indexOf('.') === -1 && str[i].indexOf('[') === -1) {//Tag
element = element.getElementsByTagName(str[i])[0];
}
else if (str[i].indexOf('[') === 0 && str[i].indexOf('=') === -1) {//属性
temp = str[i].replace('[', '').replace(']', '');
//console.log(temp)
//console.log(element.length,element)
//console.log(doc.length)
for (var element = element.getElementsByTagName('*'), j = 0; j < element.length; j++) {
if (element[j].hasAttribute(temp) === true) {
element = element[j];
}
}
}
else {//属性值
temp = str[i].replace('[', '').replace(']', '');
temp = temp.split('=');
element = element.getElementsByTagName('*');
for (var j = 0, l = element.length - 1; j < l; j++) {
console.log('j=' + j, 'element.length=' + l);
if (element[j].attributes.length != 0) {
//var xxx = element[j].attributes.length - 1;
console.log('j=' + j);
//for (var i = 0; i < xxx; i++) {
console.log('j=' + j);
if (element[j].attributes[temp[0]] != undefined && element[j].attributes[temp[0]].value === temp[1]) {
console.log('j=' + j);
element = element[j];
}
//}
}

}
}
}
return element;
}
```