常见手撕代码

1.实现兼容IE的事件处理程序

//兼容IE的事件处理程序
function addEventListener(ele,type,callback){
    if(document.addEventListener){
        ele.addEventListener(type,callback);
    } else if(document.attachEvent){
        function wrapper(){
            let event=window.event;
            event.target=event.srcElement;
            callback.call(ele,event);
        }
        ele.attachEvent('on'+type,wrapper);
    }
}

2.编写深度克隆函数

function clone(obj){
    if(typeof obj!=='object' || obj===null){
        return obj;
    }

    if('cloneNode' in obj){
        return obj.cloneNode(true);
    }

    if(Object.prototype.toString.call(obj)==='[object Date]'){
        return new Date(obj.getTime());
    }

    let res=Array.isArray(obj)?[]:
        obj.constructor?new obj.constructor():{};

    for(let key in obj){
        res[key]=clone(obj[key]);
    }

    return res;
}