掌握JavaScript破壞和傳播語法超出基礎知識

本文介紹了JavaScript中解構和擴展運算符的高級用法，重點包括：1. 使用帶默認值的解構避免undefined錯誤，並支持表達式及嵌套結構；2. 利用擴展運算符實現對象與數組的不可變更新，簡化條件屬性插入；3. 結合解構與剩餘參數優化函數參數處理，提升API可維護性，這些技巧適用於真實開發場景且無需依賴庫。

Destructuring and the spread operator in JavaScript are more than just neat tricks for writing shorter code — they're powerful tools that, when used well, can make your code cleaner, more readable, and less error-prone. Once you've got the basics down, it's time to start exploring how to use them more effectively in real-world scenarios.

Destructuring with Default Values (and Why It Matters)

One of the most useful but often underused features of destructuring is setting default values. This becomes especially handy when working with APIs or configuration objects where some properties might be missing.

For example:

 const user = { name: 'Alice' };
const { name, age = 30 } = user;
console.log(age); // 30

This pattern helps avoid undefined errors and makes assumptions explicit. You can even use expressions as defaults:

 const getUser = () => ({ name: 'Bob' });
const { name, id = Math.random() } = getUser();

Default values aren't just for primitive types — you can assign defaults to arrays or nested objects too:

 const data = { results: [] };
const { results = [{ id: 1 }] } = data;

This kind of defensive coding is especially valuable when dealing with asynchronous data from APIs, where certain fields may or may not exist depending on the response.

Spread for Immutable Updates (Without Libraries)

Immutability is a big deal in state management, especially in React or Redux-style apps. The spread operator lets you update objects or arrays without mutating the original.

Updating an object:

 const user = { name: 'John', age: 25 };
const updatedUser = { ...user, age: 26 };

Updating an array:

 const list = [1, 2, 3];
const newList = [...list.slice(0, 1), 99, ...list.slice(2)];
// [1, 99, 3]

You can also insert elements conditionally using a clever trick:

 const isAdmin = true;
const user = {
  name: 'Eve',
  ...(isAdmin && { role: 'admin' })
};

This avoids messy logic for adding optional keys to an object and keeps your updates clean and predictable.

Combining Destructuring and Spread for Flexible Functions

Function parameters become much more expressive when you mix destructuring with rest/spread. It's perfect for functions that accept many optional arguments.

Instead of this:

 function setupUser(name, age, role, isActive) { ... }

You can do:

 function setupUser({ name, age, role = 'user', isActive = true }) {
  // function body
}

And call it like:

 setupUser({ name: 'Charlie', age: 34 });

You can also combine it with the rest operator:

 function logOptions({ color, size, ...rest }) {
  console.log(`Color: ${color}, Size: ${size}`);
  console.log('Other options:', rest);
}

This pattern scales better and makes your API easier to maintain over time.

These patterns don't require any libraries or special tooling — just plain JavaScript. Once you get comfortable with them, you'll find yourself reaching for these tools regularly in both small and large applications.

基本上就這些。

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