通过属性复制实现继承

浅复制，如果属性是对象或者数组的时候，可能会导致以外

function extend(parent, child) {
    var i;
    child = child || {};
    for (i in  parent) {
        if (parent.hasOwnProperty(i)) {
            child[i] = parent[i];
        }
    }
    return child;
}
var dad = {name:"jie"};
var kid = extend(dad);
console.log(kid.name);  //jie

var dad ={
    counts:[1,2,3],
    reads:{paper:true}
}
var kid = extend(dad);
//处理数组和对象的之后，这种浅复制可能导致意外发生
kid.counts.push(4);
kid.reads.paper = false;
console.log(dad.counts);  //[ 1, 2, 3, 4 ]
console.log(dad.reads);   //{ paper: false }

深度复制，解决复制对象或者数组出现的问题。

//深度复制实现,利用了递归方法
function extendDeep(parent, child) {
    var i,
        toStr = Object.prototype.toString,
        astr = "[object Array]";
    child = child || {};

    for (i in parent) {
        if (parent.hasOwnProperty(i)) {
            if (typeof parent[i] === "object") {
                child[i] = (toStr.call(parent[i] === astr)) ? [] : {};
                extendDeep(parent[i], child[i]);
            } else {
                child[i] = parent[i];
            }
        }
    }
    return child;
}
var dad = {
    counts: [1, 2, 3],
    reads: {paper: true}
};
var kid = extendDeep(dad);

kid.counts.push(4);
console.log(kid.counts);  //[ 1, 2, 3, 4 ]
console.log(dad.counts);  //[ 1, 2, 3 ]
console.log(dad.reads === kid.reads);  //false