JavaScript中document.querySelector与querySelectorAll详解

1 document.getElementById("");
2 document.getElementsByClassName();
3 document.getElementsByTagName();

var doc=document;
var box=doc.getElementById("box");
var li=box.getElementsByTagName("li");
var surfaces=box.getElementsByClassName("surfaces");

var node = document.querySelector(“#lover”); 
// 获取文档中的第一个id=lover的元素
var node = document.querySelector(“.lover”); 
// 获取文档中的第一个class=“lover"的元素
var node = document.querySelector(“p.lover”); 
// 获取class=“lover” 的第一个p元素
var node = document.querySelector(“a[target]”);
// 获取第一个带target属性的a元素
var element = document.querySelector(‘.foo,.bar');
//返回带有foo或者bar样式类的首个元素
document.querySelector(“body”).style=”"; 
// 移除style属性
document.querySelector(“h2,h3”).style.backgroundColor = “blue”;
//为文档的第一个h2元素添加背景颜色，但是，如果文档中

var x = document.querySelectorAll("a[target]");
var i;
for (i = 0; i < x.length; i++) {
x[i].style.border = "10px solid red";
}

-------------------------------------------
let t0 = window.performance.now();
let li = document.querySelectorAll('li');
console.log("li 的数量", li.length);
for (let i = 0; i < li.length; i++) {
    li[i].textContent = i;
}
let t1 = window.performance.now();
console.log("耗时" + (t1 - t0) + "毫秒");

<div id="box">

<ul>
<li data-href='http://www.qq.com'>tagname 111</li>
<li class="surfaces">这是clase? 222</li>
<li class="surfaces">这是class333</li>
<li class="surfaces" data-href='http://www.baidu.com'>这是class444</li>
</ul>

</div>
<br>

document.getElementById("box").addEventListener("click", function(){
var attr=document.querySelectorAll('[data-href]');
console.log(attr);
},!1);

<input type="checkbox" name="gender" value="male" checked>
<input type="checkbox" name="gender" value="female">

<div lang="en"><q>This English quote has a <q>nested</q> quote inside.</q></div>
<div lang="fr"><q>This French quote has a <q>nested</q> quote inside.</q></div>
<div lang="de"><q>This German quote has a <q>nested</q> quote inside.</q></div>

<input type="text" placeholder="我是占位符">
<input type="text" placeholder="我是占位符" value="我的 value 遮盖了占位符">

let target = document.querySelector('input[type="checkbox"]:checked');
console.log('使用 querySelector 查找 ', target)

let fr = document.querySelector('div:lang(fr)');
console.log('使用 querySelector 查找 ', fr);

let pl = document.querySelector('input:placeholder-shown');
console.log('使用 querySelector 查找 ', pl);

<div id="box">
<ul>
<li >tagname 111</li>
<li class="surfaces">这是clase 222</li>
<li class="surfaces">这是class333</li>
<li class="surfaces">这是class444</li>
</ul>
</div>

--------------------------------------------------------------------------

var query_id=query('#box'); //dom id 
var query_class=query('.surfaces'); // dom class 
var query_tagname=query('li') //dom 标签

console.log('query'+query_id.innerHTML); //

console.log('query'+query_class.innerHTML); 第一个222

console.log('query'+query_tagname.innerHTML); 第一个222

--------------------------------------------------------------------------

1 var query = document.querySelector.bind(document); //单个的
var query_id=query('#box'); //dom id
var query_class=query('.surfaces'); // dom class
var query_tagname=query('li') //dom 标签
query_id.addEventListener('click',function(){
console.log('click_query_id'+this.innerHTML);   //click surfaces 2222
});

query_class.addEventListener('click',function(){
var e=e||window.event;
console.log('click_query_class'+this.innerHTML); //click surfaces 2222
e.stopPropagation();
});

query_tagname.addEventListener('click', function(e){
var e=e||window.event;
console.log('click_query_tagname' + this.innerHTML); //click surfaces 2222
e.stopPropagation();
});