2的n次方

1
2
3
1 << 2 // 4
1 << 3 // 8
1 << 4 // 16

判断n是否是2的整数幂

1
2
3
4
5
6
// n & (n - 1) === 0，则n是2的整数幂
const isPowerOf2 = n => (n & (n - 1)) === 0

isPowerOf2(2) // true
isPowerOf2(3) // false
isPowerOf2(4) // true

开关

1
2
3
4
let toggle = 0;
toggle ^= 1 // toggle: 1
toggle ^= 1 // toggle: 0
toggle ^= 1 // toggle: 1

取整

1
2
3
4
5
6
let num = 3.14
console.log(~~num) // 3
console.log(num | 0) // 3
console.log(num << 0) // 3
console.log(num >> 0) // 3
// 大数慎用

符号判断

1
2
3
4
5
6
(3 ^ -5) >= 0 // false
(-3 ^ -5) >= 0 // true
(-3 ^ 5) >= 0 // false
// 此方法不适用于0, -0
(1 ^ -0) >= 0 // true
(-1 ^ -0) >= 0 // false

评分

1
2
3
4
const rate = r => '★★★★★☆☆☆☆☆'.slice(5 - r, 10 - r)

rate(0) // ☆☆☆☆☆
rate(3) // ★★★☆☆

随机整数 [min, max)

1
2
3
4
5
function getRandomInt(min, max) {
  const minCeiled = Math.ceil(min);
  const maxFloored = Math.floor(max);
  return Math.floor(Math.random() * (maxFloored - minCeiled) + minCeiled);
}

Hex随机色

1
2
3
const randomHexColor = () => `#${Math.random().toString(16).slice(2, 8).padEnd(6, "0")}`;
const hexColor = randomHexColor();
console.log(`%c${hexColor}`, `color:${hexColor}`);

RGB随机色

1
2
3
const randomRGBColor = () => `rgb(${getRandomInt(0, 256)}, ${getRandomInt(0, 256)}, ${getRandomInt(0, 256)})`;
const rgb = randomRGBColor();
console.log(`%c${rgb}`, `color:${rgb}`);

文件大小单位转换

1
2
3
4
5
6
7
8
9
function autoSizeUnit(byte) {
  var units = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB', 'BB'];
  var unitIndex = 0;
  while (byte >= 1024 && unitIndex < units.length - 1) {
    byte /= 1024;
    unitIndex++;
  }
  return `${byte.toFixed(2)} ${units[unitIndex]}`;
}

小驼峰字符串

1
2
3
4
5
6
7
8
9
function camelCase(str) {
  function capitalizeFirstLetter(string) {
    return string.charAt(0).toUpperCase() + string.slice(1);
  }
  const tokens = str.split(/[^a-zA-Z0-9]|((?<=\D)\B(?=\d))|((?<=\d)\B(?=[a-zA-Z]))/g).filter(Boolean)
  return tokens[0] + tokens.slice(1).map(capitalizeFirstLetter).join("")
}

console.log(camelCase("_lsd33432ds0-a-dk1")); // lsd33432Ds0ADk1

滑动Chunk

1
2
3
4
5
6
7
8
9
function slidingChunk<T>(array: T[], size: number) {
  if (!Array.isArray(array)) return []
  if (size <= 0) return []
  if (size > array.length) return [array]

  return Array.from({ length: array.length - size + 1 }, (_, i) => array.slice(i, i + size))
}

console.log(slidingChunk([1,2,3,4], 2)); // [[1,2],[2,3],[3,4]]

排列数 P(n,m)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
const getPermutations = <T>(array: T[], m: number): T[][] => {
  if (m > array.length || m < 0) return []
  if (m === 0) return [[]]

  const result: T[][] = []

  const backtrack = (current: T[], used: boolean[]) => {
    if (current.length === m) {
      result.push([...current])
      return
    }

    for (let i = 0; i < array.length; i++) {
      if (used[i]) continue

      current.push(array[i]!)
      used[i] = true
      backtrack(current, used)
      current.pop()
      used[i] = false
    }
}

console.log(getPermutations([1, 2, 2], 2)); // 输出: [[1, 2], [2, 1], [2, 2]]