俗話說的好，一天一蘋果，醫生遠離我
一天一 JS，What the f*ck JavaScript？
small steps every day - 記錄著新手村日記
今天來做 JavaScript reference 與 copy 了解 JavaScript 是怎麼運作的
就依下面的題目一題一題做吧！(我也看不懂如何分題目...
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>JS Reference VS Copy</title>
</head>
<body>
<script>
// start with strings, numbers and booleans
// Let's say we have an array
const players = ['Wes', 'Sarah', 'Ryan', 'Poppy'];
// and we want to make a copy of it.
// You might think we can just do something like this:
// however what happens when we update that array?
// now here is the problem!
// oh no - we have edited the original array too!
// Why? It's because that is an array reference, not an array copy. They both point to the same array!
// So, how do we fix this? We take a copy instead!
// one way
// or create a new array and concat the old one in
// or use the new ES6 Spread
// now when we update it, the original one isn't changed
// The same thing goes for objects, let's say we have a person object
// with Objects
const person = {
name: 'Wes Bos',
age: 80
};
// and think we make a copy:
// how do we take a copy instead?
// We will hopefully soon see the object ...spread
// Things to note - this is only 1 level deep - both for Arrays and Objects. lodash has a cloneDeep method, but you should think twice before using it.
</script>
</body>
</html>
首先，首先，從字串、數字、布林開始：
<script>
// start with strings, numbers and booleans
let age = 100;
let age2 = age;
console.log(age, age2);
// 100 100
age = 200;
console.log(age, age2);
// 200 100
let name = 'Wes';
let name2 = name;
console.log(name, name2);
// Wes Wes
name = 'wesley';
console.log(name, name2);
//wesley Wes
</script>
複製陣列的三種方式
<script>
// 陣列
const players = ['Wes', 'Sarah', 'Ryan', 'Poppy'];
// 我們希望複製這個陣列
const team = players;
console.log(players, team);
// 也許你應該覺得就長這樣吧:
// team[3] = 'Lux';
// 但是當我們更新陣列的時候呢？
// 問題就...
// 我們原本的陣列也被更改到了～
// 因為這不是複製、都在記憶體中對應到同一個陣列
// one way
const team2 = players.slice();
// second
const team3 = [].concat(players);
// or use the new ES6 Spread
const team4 = [...players];
team4[3] = 'heeee hawww';
console.log(team4);
//["Wes", "Sarah", "Ryan", "heeee hawww"]
</script>
物件的複製
Object.assign() 則不會<script>
// with Objects
const person = {
name: 'Wes Bos',
age: 80
};
// and think we make a copy:
// const captain = person;
// captain.number = 99;
// how do we take a copy instead?
const cap2 = Object.assign({}, person, { number: 99, age: 12 });
console.log(cap2);
// We will hopefully soon see the object ...spread
// const cap3 = {...person};
// Things to note - this is only 1 level deep - both for Arrays and Objects. lodash has a cloneDeep method, but you should think twice before using it.
const wes = {
name: 'Wes',
age: 100,
social: {
twitter: '@wesbos',
facebook: 'wesbos.developer'
}
};
console.clear();
console.log(wes);
const dev = Object.assign({}, wes);
const dev2 = JSON.parse(JSON.stringify(wes));
</script>
<script>
// start with strings, numbers and booleans
// let age = 100;
// let age2 = age;
// console.log(age, age2);
// age = 200;
// console.log(age, age2);
// let name = 'Wes';
// let name2 = name;
// console.log(name, name2);
// name = 'wesley';
// console.log(name, name2);
// Let's say we have an array
const players = ['Wes', 'Sarah', 'Ryan', 'Poppy'];
// and we want to make a copy of it.
const team = players;
console.log(players, team);
// You might think we can just do something like this:
// team[3] = 'Lux';
// however what happens when we update that array?
// now here is the problem!
// oh no - we have edited the original array too!
// Why? It's because that is an array reference, not an array copy. They both point to the same array!
// So, how do we fix this? We take a copy instead!
const team2 = players.slice();
// one way
// or create a new array and concat the old one in
const team3 = [].concat(players);
// or use the new ES6 Spread
const team4 = [...players];
team4[3] = 'heeee hawww';
console.log(team4);
const team5 = Array.from(players);
// now when we update it, the original one isn't changed
// The same thing goes for objects, let's say we have a person object
// with Objects
const person = {
name: 'Wes Bos',
age: 80
};
// and think we make a copy:
// const captain = person;
// captain.number = 99;
// how do we take a copy instead?
const cap2 = Object.assign({}, person, { number: 99, age: 12 });
console.log(cap2);
// We will hopefully soon see the object ...spread
// const cap3 = {...person};
// Things to note - this is only 1 level deep - both for Arrays and Objects. lodash has a cloneDeep method, but you should think twice before using it.
const wes = {
name: 'Wes',
age: 100,
social: {
twitter: '@wesbos',
facebook: 'wesbos.developer'
}
};
console.clear();
console.log(wes);
const dev = Object.assign({}, wes);
const dev2 = JSON.parse(JSON.stringify(wes));
</script>
本刊同步於個人網站：http://chestertang.site/
本次範例程式碼原作者來源：https://tinyurl.com/yavm5f5n
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