Rest參數(shù)允許將多個參數(shù)收集為數(shù)組，簡化了處理不定數(shù)量參數(shù)的函數(shù)編寫。例如，在sum函數(shù)中使用...numbers可捕獲所有參數(shù)並作為數(shù)組處理，進而可用reduce等方法求和；與arguments對像不同，rest參數(shù)是真正的數(shù)組且僅包含未命名參數(shù)；此外，rest參數(shù)必須位於函數(shù)參數(shù)列表的最後位置。 1. 使用...語法將參數(shù)收集為數(shù)組。 2. 可直接應(yīng)用map、filter等數(shù)組方法。 3. rest參數(shù)必須放在參數(shù)列表末尾。

Rest parameters in JavaScript are a way to represent an indefinite number of arguments as an array. This feature is super handy when you're writing functions that need to accept a variable number of inputs.

Using Rest Parameters in Functions

When you use the rest parameter syntax ( ...parameterName ), it collects all remaining arguments into a real array. This makes it easier to work with them using array methods like map , filter , or reduce .

For example:

 function sum(...numbers) {
  return numbers.reduce((total, num) => total num, 0);
}

console.log(sum(1, 2, 3)); // Output: 6

Here's what happens:

• The rest parameter ...numbers captures all the arguments passed to the function.
• It turns them into a proper array called numbers .
• You can then use .reduce() to add them up without any hassle.

This is really useful when you don't know how many values someone will pass into your function.

Difference Between Rest Parameters and arguments

It's easy to confuse rest parameters with the older arguments object in JavaScript.

The main differences are:

• arguments isn't a real array — it's an array-like object, so you can't directly use array methods on it.
• Rest parameters are actual arrays, which means you can do things like map or filter right away.
• The arguments object includes all arguments passed to the function, while rest parameters only include the ones that don't have their own named parameter.

So if you're writing modern JavaScript, rest parameters are usually the better choice for handling multiple inputs.

Rest Parameters Must Be the Last Parameter

One important rule: the rest parameter has to be the last one in the function definition. Otherwise, JavaScript won't know where the rest begins.

For example:

 function logItems(prefix, ...items) {
  console.log(prefix, items);
}

In this case:

• The first argument becomes prefix
• All remaining arguments are collected into the items array

But if you try to do something like this:

 function badExample(...items, suffix) { // Syntax error!
  // ...
}

You'll get an error because rest parameters can't come before other named parameters.

Summary

So to recap quickly:

• Rest parameters let you capture multiple arguments into an array.
• They're more flexible and powerful than the old arguments object.
• Always place them at the end of your function's parameter list.

基本上就這些.

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