# concat

`concat` 用来合并两个或者多个数组。`concat` 不影响原始数组，会返回一个新数组

```javascript
const letters = ['a', 'b', 'c'];
const numbers = [1, 2, 3];

letters.concat(numbers);
// result in ['a', 'b', 'c', 1, 2, 3]
```

### concat 可以传入数值

```javascript
const letters = ['a', 'b', 'c'];

const alphaNumeric = letters.concat(1, [2, 3]);

console.log(alphaNumeric); 
// results in ['a', 'b', 'c', 1, 2, 3]
```

### concat 内部是对原对象的引用，原对象改变，concat的返回对象也改变

```javascript
const num1 = [[1]];
const num2 = [2, [3]];

const numbers = num1.concat(num2);

console.log(numbers);
// results in [[1], 2, [3]]

// modify the first element of num1
num1[0].push(4);

console.log(numbers);
// results in [[1, 4], 2, [3]]
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mm.ricky.moe/javascript/es6-han-shu/concat.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.