浅拷贝Shallow Copy VS 深拷贝Deep Copy

浅拷贝：指向同一个记忆体，原始值与新複製出来的值会连动深拷贝：为切断之间的关联性，複製即产生一个新的记忆体存放，所以当改动複製出来的值时，原始值就不会随着被更动在js中，物件与阵列的複製皆属于call by reference，所以如果以原始型别複製的方法，会有改写原始值的问题

//原始型别如数值let a = 7 let b = aa = 8console.log(a, b) //8, 7

由于原始型别複製是call by value(参考值，但创自己新的记忆体空间，指向的位置不同，所以改变a对b不会有影响)但在阵列複製是call by reference的情况下:

const players = ['emma', 'wilee', 'stella', 'jenny']const team = playersteam[3] = 'julia'console.log(players, team)// ['emma', 'wilee', 'stella', 'julia']// ['emma', 'wilee', 'stella', 'julia']

team一改，players会跟着改，因为两个物件指向同一个记忆体，基本上他们两个是同一个东西，只是用不同名称来称呼同一个东西阵列如何切断连动关係，实现深拷贝

const players = ['emma', 'wilee', 'howord', 'jenny']const team2 = [...players]const team3 = [].concat(players)const team4 = Array.from(players)cosnt team5 = players.slice()team5[3] = 'julia'team2[3] = 'cash'team3[3] = 'miya'team4[3] = 'sylar'console.log(players, team2, team3, team4, team5);// ['emma', 'wilee', 'stella', 'jenny']// ['emma', 'wilee', 'stella', 'cash']// ['emma', 'wilee', 'stella', 'miya']// ['emma', 'wilee', 'stella', 'sylar']// ['emma', 'wilee', 'stella', 'julia']以上四种方法都可以让複製值存放在新的记忆体，互相不干扰

接下来看物件，同样是call by reference，但深拷贝较複杂，易混淆

const person = {name: 'julia'age: 40}const driver = persondriver.gentle = 'female'console.log(person, driver)//可以看到原本的person跟driver连动

用以下这两种作法看是否能达到深拷贝Object.assign()... spread syntax

const person = {name: 'julia',age: 40}const driver = Object.assign({}, person)driver.name = 'stella'const driver2 = {...person}driver2.name = 'amy'console.log(person, driver, driver2)//看起来似乎有成功但...

如果物件内又包一个物件（nested object），其物件仍指向同一个记忆体，所以这2种做法只达到最外层深拷贝，里面还是一样，

const julia = {      name: 'julia',      age: 40,      social: {        facebook: '@aaa',        instagram: '@bbb'      }    }    const dev = Object.assign({}, julia)    dev.social.instagram = '@ccc'    console.log(julia, dev);   //可以看到两个instagram连动    //...也是得到一样连动的结果

JSON.parse(JSON.stringfy())解决上面连动问题，达到深拷贝效果然而有两个雷物件中有function物件中有型别问题时参考影片：JavaScript Objects: Shallow and Deep Copy | All You Need to Know in 10 mins!如果发生上述两种情况，只能额外安装lodash解决

const julia = {      name: 'julia',      age: 40,      social: {        facebook: '@aaa',        instagram: '@bbb'      }    }    const dev = JSON.parse(JSON.stringfy(julia))    dev.social.instagram = '@ccc'    console.log(julia, dev);