选择器模块之传统做法
var tag = function (tag){
return document.getElementsByTagName(tag);
}
var id = function (id){
return document.getElementById(id);
}
var className = function (className){
return document.getElementsByClassName(className);
}
由浅入深之tag方法
这是html部分代码
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<style type="text/css">
div, p {
width: 200px;
height:50px;
border:1px dashed red;
margin: 10px 0;
}
</style>
</head>
<body>
<div></div>
<div></div>
<p></p>
<p></p>
</body>
//例如给div盒子添加背景色我们可能会这么做
var divs = tag('div');
var each = function (arr){
for(var i = 0;i< arr.length;i++){
arr[i].style.backgroundColor = 'pink';
}
}
each(divs);
//也可能会这么做
var list = tag('div');
var each = function (arr,fn){
for(var i = 0;i<arr.length;i++){
if(fn.call(arr[i],i,arr[i]) === false ){//等于false时，终止循环
break;
}
}
}
each(list,function(){
this.style.backgroundColor = 'yellow';
})
//上式的fn.call(arr[i],i,arr[i]) === false，下面函数也用到这种调用方式，可以做下比较
var arr = [ 1, 2, 3, 4, 3, 5];
var each = function ( arr, fn ) {
for ( var i = 0; i < arr.length; i++ ) {
if ( fn( i, arr[ i ] ) === false ) {
break;
}
}
}; var index = -1;
each( arr, function ( i, v ) {
if ( v === 3 ) {
index = i;
return false;//若是break 遍历不会终止 直到遍历完
}
} );
console.log( index );//
/*var tag = function (tag){
return document.getElementsByTagName(tag);
}*/
//以上这种写法的缺点是每次获得元素后又要返回，以至于造成浏览器性能的损耗
//为了简化开发，可以将获得的数组合并到一个数组中,这也是jq中所用到的
var getTag = function ( tag, results ) {
results = results || [];
results.push.apply( results, document.getElementsByTagName( tag ) );
return results;
};
var list = getTag('div');
list = getTag('p',list);//如果再获得p标签，可以这么写
var each = function (arr,fn){
for(var i = 0;i<arr.length;i++){
if(fn.call(arr[i],i,arr[i]) === false ){//等于false时，终止循环
break;
}
}
}
/*each(list,function(){
this.style.backgroundColor = 'lightgreen';
})*/
each(getTag('p',getTag('div')),function(){
this.style.backgroundColor = 'lightgreen';
})
进一步整合以上方法 上面方法也只能获得指定标签元素，需求是要兼顾获取标签、id和类名
思路：单独写一个函数，如果再函数中想获得标签、id和类名，直接调用其方法即可
在此用到的html和样式对以下操作的验证
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<style type="text/css">
div, p {
width: 200px;
height:50px;
border:1px dashed red;
margin: 10px 0;
}
</style>
</head>
<body>
<div id="id">id</div>
<div class="class"></div>
<p></p>
<p></p>
</body>
1、分别列出获取标签、id、类名对应的方法
var getTag = function ( tag, results ) {
results = results || [];
results.push.apply( results, document.getElementsByTagName( tag ));
return results;
};
var getId = function ( id, results ) {
results = results || [];
results.push( document.getElementById( id ) );//此处是单个数据，无须用apply方法
return results;
};
var getClass = function ( className, results ) {
results = results || [];
results.push.apply( results, document.getElementsByClassName( className ) );
return results;
};
2、书写get方法，判断调用以上哪一种方法
var get = function ( selector, results ) {
results = results || [];
// 1 2 3 4
var rquickExpr = /^(?:#([\w-]+)|\.([\w-]+)|([\w]+)|(\*))$/,//正则表达式
m = rquickExpr.exec( selector );//正则匹配
if ( m ) {//判断是否匹配成功（此处if判断可以省略）
if ( m[ 1 ] ) {
results = getId( m[ 1 ], results );
} else if ( m[ 2 ] ) {
results = getClass( m[ 2 ], results );
} else if ( m[ 3 ] ) {
results = getTag( m[ 3 ], results );
} else if ( m[ 4 ] ) {
results = getTag( m[ 4 ], results );
}
//因为标签元素选择器和通配符选择器所调用的方法一样，所以可以进行整合如下
/*if ( m[ 1 ] ) {
results = getId( m[ 1 ], results );
} else if ( m[ 2 ] ) {
results = getClass( m[ 2 ], results );
} else {
results = getTag( m[ 3 ] || "*", results )
}*/
}
return results;//返回results
};
上面是用正则匹配字符串的，如果不用正则如何实现
var get = function(selector, results) {
results = results || [];
if (selector === '*') {
return results = getTag(selector, results);
} else {
var firstChar = selector.charAt(0);
switch (firstChar) {
case '.':
results = getClass(selector.slice(1), results);
break;
case '#':
results = getId(selector.slice(1), results);
break;
default:
results = getTag(selector, results);
break;
}
return results;
}
}
3、书写each方法遍历所获得的元素数组
var each = function ( arr, fn ) {
for ( var i = 0; i < arr.length; i++ ) {
if ( fn.call( arr[ i ], i, arr[ i ] ) === false ) {
break;
}
}
};
4、调用each方法，执行验证相关需求的操作
each( get( "#id" ), function () {
this.style.backgroundColor = 'lightgreen';
} );
最后把以上方法整合在一起，如下
// 注释: 对基本选择器方法的封装
var getTag = function ( tag, results ) {
results = results || [];
results.push.apply( results, document.getElementsByTagName( tag ) );
return results;
}; var getId = function ( id, results ) {
results = results || [];
results.push( document.getElementById( id ) );
return results;
}; var getClass = function ( className, results ) {
results = results || []; if ( document.getElementsByClassName ) {
results.push.apply( results, document.getElementsByClassName( className ) );
} else {
each( getTag( '*' ), function ( i, v ) {
if ( ( ' ' + v.className + ' ' )
.indexOf( ' ' + className + ' ' ) != -1 ) {
results.push( v );
}
} );
}
return results;
}; // 对each方法循环的封装
var each = function ( arr, fn ) {
for ( var i = 0; i < arr.length; i++ ) {
if ( fn.call( arr[ i ], i, arr[ i ] ) === false ) {
break;
}
}
}; // 通用的get方法
var get = function ( selector, results ) {
results = results || [];
var rquickExpr = /^(?:#([\w-]+)|\.([\w-]+)|([\w]+)|(\*))$/,
m = rquickExpr.exec( selector ); if ( m ) { if ( m[ 1 ] ) {
results = getId( m[ 1 ], results );
} else if ( m[ 2 ] ) {
results = getClass( m[ 2 ], results );
} else if ( m[ 3 ] ) {
results = getTag( m[ 3 ], results );
} else if ( m[ 4 ] ) {
results = getTag( m[ 4 ], results );
} }