用30秒看懂127个实用的JavaScript代码片段（二）

## **22. 展平多维数组** 

通过递归的形式，将多维数组展平成一维数组。

```javascript
const flatten = (arr) => {
  let result = [];
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      result = result.concat(flatten(arr[i]));
    } else {
      result.push(arr[i]);
    }
  }
  return result;
};

const multidimensionalArray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
const flattenedArray = flatten(multidimensionalArray);
console.log(flattenedArray); // [1, 2, 3, 4, 5, 6, 7, 8, 9]
```

## **23. 去除对象中的重复属性** 

去重对象的属性，如果对象中含有重复的属性，以前面的属性值为准。

```javascript
const removeDuplicateProperties = (obj) => {
  const seen = {};
  const result = {};
  for (let key in obj) {
    if (!seen[key]) {
      seen[key] = true;
      result[key] = obj[key];
    }
  }
  return result;
};

const objectWithDuplicateProperties = {
  name: 'John Doe',
  age: 30,
  name: 'Jane Doe',
  city: 'New York'
};
const objectWithoutDuplicateProperties = removeDuplicateProperties(objectWithDuplicateProperties);
console.log(objectWithoutDuplicateProperties); // { name: 'John Doe', age: 30, city: 'New York' }
```

## **24. 获取数组中最大的数字** 

获取数组中最大的数字，如果数组为空或不包含任何数字，则返回undefined。

```javascript
const max = (arr) => {
  if (arr.length === 0 || !arr.every(Number.isFinite)) {
    return undefined;
  }
  let maxNumber = arr[0];
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] > maxNumber) {
      maxNumber = arr[i];
    }
  }
  return maxNumber;
};

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const largestNumber = max(numbers);
console.log(largestNumber); // 9
```

## **25. 获取数组中最小的数字** 

获取数组中最小的数字，如果数组为空或不包含任何数字，则返回undefined。

```javascript
const min = (arr) => {
  if (arr.length === 0 || !arr.every(Number.isFinite)) {
    return undefined;
  }
  let minNumber = arr[0];
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] < minNumber) {
      minNumber = arr[i];
    }
  }
  return minNumber;
};

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const smallestNumber = min(numbers);
console.log(smallestNumber); // 1
```

## **26. 检查数组是否包含某个元素** 

检查数组是否包含某个元素，如果包含则返回true，否则返回false。

```javascript
const includes = (arr, element) => {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === element) {
      return true;
    }
  }
  return false;
};

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const element = 5;
const isElementPresent = includes(numbers, element);
console.log(isElementPresent); // true
```

## **27. 随机打乱数组** 

随机打乱数组的元素顺序，但不改变数组的长度。

```javascript
const shuffle = (arr) => {
  for (let i = 0; i < arr.length; i++) {
    const randomIndex = Math.floor(Math.random() * arr.length);
    const temp = arr[i];
    arr[i] = arr[randomIndex];
    arr[randomIndex] = temp;
  }
  return arr;
};

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const shuffledNumbers = shuffle(numbers);
console.log(shuffledNumbers); // [9, 2, 8, 6, 4, 5, 3, 7, 1]
```