浏览器兼容设置

都以点击事件 onclick 为例：

事件对象获取

document.onclick = function(ev) {
        let e = ev || window.event;
}

获取键码

let w = e.which || e.keyCode;

目标对象 / 触发对象

button.onclick = function() {
	let target = e.target || window.event.srcElement;
}

阻止超链接默认行为的函数

e 为获取到的事件

function preDef(e) {
	if(e.preventDefault) {
		e.preventDefault();
	} else {
		window.event.returnValue = false;
	}
}

事件监听器

function addEvent(node,evenType,funName) {
    if(node.addEventListener) {
        node.addEventListener(evenType, funName,false);
    } else {
        node.attachEvent('on' + evenType, funName);
    }
}

function removeEvent(node,evenType,funName) {
    if(node.removeEventListener) {
        node.removeEventListener(evenType, funName,false);
    } else {
        node.detachEvent('on' + evenType, funName);
    }
}

获取当前窗口的宽高

let Width = document.documentElement.clientWidth || document.body.clientWidth;
let Height = document.documentElement.clientHeight || document.body.clientHeight;

拖拽封装

普通拖拽封装

function drag(node) {
    node.onmousedown = function(ev) {
        let e = ev || window.event;

        // 获取鼠标到 node 左上角的相对位置
        let offSetX = e.clientX - node.offsetLeft;
        let offSetY = e.clientY - node.offsetTop;

        // 鼠标移动时，计算 node 左上角应该在的位置
        document.onmousemove = function(ev) {
            let e = ev || window.event;
            node.style.left = e.clientX - offSetX + 'px';
            node.style.top = e.clientY - offSetY + 'px';
        }
    }

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

限制出界的拖拽封装

function limitDrag(node) {
    node.onmousedown = function (ev) {
        let e = ev || window.event;

        // 获取鼠标到 node 左上角的相对位置
        let offSetX = e.clientX - node.offsetLeft;
        let offSetY = e.clientY - node.offsetTop;
   
        document.onmousemove = function (ev) {
            let e = ev || window.event;
            // 鼠标移动时，计算 node 左上角应该在的位置
            let x = e.clientX - offSetX;
            let y = e.clientY - offSetY;

            // 限制出界
            // 获取当前窗口的宽高
            let Width = document.documentElement.clientWidth || document.body.clientWidth;
            let Height = document.documentElement.clientHeight || document.body.clientHeight;
            if (x <= 0) {
                x = 0;
            }
            if (x >= Width - node.offsetWidth) {
                x = Width - node.offsetWidth
            }
            if (y <= 0) {
                y = 0;
            }
            if (y >= Height - node.offsetHeight) {
                y = Height - node.offsetHeight
            }
            node.style.left = x + 'px';
            node.style.top = y + 'px';
        }
    }

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

针对拖拽封装的小栗子：
https://blog.csdn.net/Web_blingbling/article/details/107868162