事件对象

var box = document.querySelector('.box');
box.onmouseover = function(event){
    // console.log(event);
    console.log(window.event.type);
    var e = event || window.event;
    
}

• 阻止冒泡

var big = document.querySelector('.big')
var middle = document.querySelector('.middle')
var small = document.querySelector('.small')
big.onclick = function(){
    console.log("大");
}
middle.onclick = function(){
    console.log("中");
}
small.onclick = function(e){
    var e = e || window.event;
    console.log("小");

    // 需要事件对象来阻止冒泡 - e.stopPropagation()
    // e.stopPropagation()
    // 低版本ie中
    // e.cancelBubble = true

    兼容的阻止冒泡
    if(e.stopPropagation){
        e.stopPropagation()
    }else{
        e.cancelBubble = true
    }
}

• 获取鼠标的按键信息

var box = document.querySelector('.box')
box.onmousedown = function(e){
    var e = e || window.event;
    console.log(e);
    console.log(e.button);
}

• 键盘码

window.onkeydown = function(e){
    // 获取键盘码
    var e = e || window.event;
    // 键盘码 - e.keyCode
    // 键盘码在低版本火狐中不兼容
    // 兼容 写法
    var keycode = e.keyCode || e.which;
    console.log(keycode);
    // 如果要判断是否按下的是a键
    // 将键盘码获取到，转成字符
    var s = String.fromCharCode(keycode)
    // console.log(s);
    // 转小写
    s = s.toLowerCase()
    console.log(s);

• 鼠标坐标点

var box = document.querySelector('.box')
document.onclick = function(e){
    var e = e || window.event;
    console.log(e);
    // e.offsetX  e.offsetY - 鼠标在当前事件源上的位置
    console.log(e.offsetX,e.offsetY);

    // e.clientX   e.clinetY  - 鼠标在浏览器中的位置
    console.log(e.clientX,e.clientY); 

    // e.pageX  e.pageY - 鼠标在整个页面中的绝对距离 - 包含了滚动过的距离
    console.log(e.pageX,e.pageY);
    console.log(document.documentElement.scrollTop);
}

拖拽div

var box = document.querySelector('.box')
box.onmousedown = function(e){
    var e = e || window.event;
    var x1 = e.offsetX;
    var y1 = e.offsetY;
    document.onmousemove = function(e){
        var e1 = e || window.event;
        var x2 = e1.pageX;
        var y2 = e1.pageY;

        var left = x2 - x1;
        var top = y2 - y1;

        box.style.left = left + "px"
        box.style.top = top + "px"
    }
}

window.onmouseup = function(){
    document.onmousemove = null
}

• 阻止默认行为
  1.事件对象

    if(e.preventDefault){
        e.preventDefault()
    }else{
        e.returnValue = false
    }

2.将链接改成 javascipt:; javascript:void(0);
3.在事件函数的最下面添加：return false

• 事件委托

var lis = document.querySelectorAll('li')
for(var i=0;i<lis.length;i++){
    lis[i].onclick = function(){
        console.log(this.innerText);
    }
}


var ul = document.querySelector('ul')
ul.onclick = function(e){
    var e = e || window.event;
    // e.target - 当前点击的最精准的子标签
    var target = e.target || e.srcElement;
    console.log(target.innerText);
}