数字常用计算操作

随机数范围

export const random = (min, max) => {
    if (arguments.length === 2) {
        return Math.floor(min + Math.random() * ((max + 1) - min))
    } else {
        return null;
    }
}
function randomNum(minNum: number, maxNum: number) {
  return parseInt(`${Math.random() * (maxNum - minNum + 1) + minNum}`, 10)
}

export const randomNum = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

小数转百分数 保留两位小数

Number(0.8965456465156 * 100).toFixed(2) + "%"

保留小数点以后 n 位

// 保留小数点以后几位，默认2位
export function cutNumber(number, no = 2) {
    if (typeof number != 'number') {
        number = Number(number)
    }
    return Number(number.toFixed(no))
}

bytes 字节单位自动转化 MB GB …等

function bytesToSize(bytes: number | string) {
  if (isString(bytes)) {
    bytes = Number(bytes)
  }
  if (bytes === 0) {
    return { size: 0, switchSize: 0, unit: 'MB' }
  }
  let sign = '+'
  if (bytes < 0) {
    bytes = Math.abs(bytes)
    sign = '-'
  }
  const k = 1024
  const units = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']
  const unitIndex = Math.floor(Math.log(bytes) / Math.log(k))
  let switchSize = bytes / Math.pow(k, unitIndex)
  if (sign === '-') {
    bytes = -bytes
    switchSize = -switchSize.toFixed(2)
  }
  return {
    size: bytes,
    switchSize: switchSize,
    unit: units[unitIndex >= units.length ? units.length - 1 : unitIndex]
  }
}

判断奇数偶数

const isEven = num => num % 2 === 0;
console.log(isEven(2));
// Result: true
console.log(isEven(3));
// Result: false

格式化金钱

项目中我们经常会遇到金钱格式化需求，或者说数字格式化一下，方便阅读（数字比较大的情况下）
比如说 999999999，直接阅读很不直观，格式化后 999,999,999

//正则
function formatPrice(price) {
  return String(price).replace(/\B(?=(\d{3})+(?!\d))/g, ',');
}
function formatPrice(price) {
  return String(price)
    .split('')
    .reverse()
    .reduce((prev, next, index) => {
      return (index % 3 ? next : next + ',') + prev;
    });
}
(999999999).toLocaleString(); // 999,999,999
// 当然还可以更秀一点
const options = {
  style: 'currency',
  currency: 'CNY',
};
(123456).toLocaleString('zh-CN', options); // ¥123,456.00

toLocaleString 可以接收两个可选参数：locales 和 options，而且这个 api 在各大浏览器通用不存在兼容问题并且这个 api 不止存在 Number 的原型上，Array、Object、Date 原型上都有这个 api，并且格式化出来的值可以根据我们传入的参数出现各种结果，参数及用法可以参考 MDN

数字转化为大写金额

const digitUppercase = (n) => {
  const fraction = ["角", "分"];
  const digit = ["零", "壹", "贰", "叁", "肆", "伍", "陆", "柒", "捌", "玖"];
  const unit = [
    ["元", "万", "亿"],
    ["", "拾", "佰", "仟"],
  ];
  n = Math.abs(n);
  let s = "";
  for (let i = 0; i < fraction.length; i++) {
    s += (
      digit[Math.floor(n * 10 * Math.pow(10, i)) % 10] + fraction[i]
    ).replace(/零./, "");
  }
  s = s || "整";
  n = Math.floor(n);
  for (let i = 0; i < unit[0].length && n > 0; i++) {
    let p = "";
    for (let j = 0; j < unit[1].length && n > 0; j++) {
      p = digit[n % 10] + unit[1][j] + p;
      n = Math.floor(n / 10);
    }
    s = p.replace(/(零.)*零$/, "").replace(/^$/, "零") + unit[0][i] + s;
  }
  return s
    .replace(/(零.)*零元/, "元")
    .replace(/(零.)+/g, "零")
    .replace(/^整$/, "零元整");
};

数字转中文数字

export const intToChinese = (value) => {
 const str = String(value);
 const len = str.length-1;
 const idxs = ['','十','百','千','万','十','百','千','亿','十','百','千','万','十','百','千','亿'];
 const num = ['零','一','二','三','四','五','六','七','八','九'];
 return str.replace(/([1-9]|0+)/g, ( $, $1, idx, full) => {
    let pos = 0;
    if($1[0] !== '0'){
      pos = len-idx;
      if(idx == 0 && $1[0] == 1 && idxs[len-idx] == '十'){
        return idxs[len-idx];
      }
      return num[$1[0]] + idxs[len-idx];
    } else {
      let left = len - idx;
      let right = len - idx + $1.length;
      if(Math.floor(right / 4) - Math.floor(left / 4) > 0){
        pos = left - left % 4;
      }
      if( pos ){
        return idxs[pos] + num[$1[0]];
      } else if( idx + $1.length >= len ){
        return '';
      }else {
        return num[$1[0]]
      }
    }
   });
}