@df8080/vue2-ui/utils/calc.js

🎨 一个基于 Vue 2 的 UI 组件库，目前主要面向微信小程序开发场景，也适用于其他移动端项目。

/** 得到小数点后数字长度 */
const digitLength = (num) => {
  if (!num) {
    return 0
  }

  const eSplit = num.toString().split(/[eE]/)
  const len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0)
  return len > 0 ? len : 0
}

/** 把错误的数据转正 strip(0.09999999999999998)=0.1 */
export const strip = (num, precision = 16) => {
  return +parseFloat(num.toPrecision(precision))
}

/** 把小数转成整数，支持科学计数法。如果是小数则放大成整数 */
export function float2Fixed(num) {
  if (!num) {
    return 0
  }

  if (num.toString().indexOf('e') === -1) {
    return Number(num.toString().replace('.', ''))
  }
  const dLen = digitLength(num)
  return dLen > 0 ? strip(num * Math.pow(10, dLen)) : num
}

/** 精确加法 */
export const plus = (...args) => {
  const [num1, num2, ...others] = args
  if (others.length > 0) {
    return plus(plus(num1, num2), others[0], ...others.slice(1))
  }
  const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)))
  return (times(num1, baseNum) + times(num2, baseNum)) / baseNum
}

/** 精确减法 */
export const minus = (num1, num2, ...others) => {
  if (others.length > 0) {
    return minus(minus(num1, num2), others[0], ...others.slice(1))
  }
  const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)))
  return (times(num1, baseNum) - times(num2, baseNum)) / baseNum
}

/** 精确乘法 */
export const times = (num1, num2, ...others) => {
  if (others.length > 0) {
    return times(times(num1, num2), others[0], ...others.slice(1))
  }
  const num1Changed = float2Fixed(num1)
  const num2Changed = float2Fixed(num2)
  const baseNum = digitLength(num1) + digitLength(num2)
  const leftValue = num1Changed * num2Changed
  return leftValue / Math.pow(10, baseNum)
}

/** 精确除法 */
export const divide = (num1, num2, ...others) => {
  if (num2 === 0) {
    return 0
  }
  if (others.length > 0) {
    return divide(divide(num1, num2), others[0], ...others.slice(1))
  }
  const num1Changed = float2Fixed(num1)
  const num2Changed = float2Fixed(num2)
  return times(num1Changed / num2Changed, Math.pow(10, digitLength(num2) - digitLength(num1)))
}

/**
 * 四舍五入,自动补0
 * @param   num	待处理数字
 * @param   decimals 需要保留的小数位
 * @return  处理后的数字
 */
export const formatRound = (num, decimals = 2) => {
  if (isNaN(num)) {
    return 0
  }
  const p1 = Math.pow(10, decimals + 1)
  const p2 = Math.pow(10, decimals)
  const absNum = Math.round((Math.abs(num) * p1) / 10) / p2
  let copyNumStr = absNum.toString()
  if (decimals) {
    if (copyNumStr.indexOf('.') > 0) {
      const _float = copyNumStr.split('.')[1]
      if (_float.length < decimals) {
        copyNumStr = absNum + new Array(decimals - _float.length).fill(0).join('')
      }
    } else {
      copyNumStr = absNum + `.${new Array(decimals).fill(0).join('')}`
    }
  }

  return num > 0 ? Number(copyNumStr) : -Number(copyNumStr)
}

/**
 * 向下取整保留x位小数
 * @param   num	待处理数字
 * @param   decimals 需要保留的小数位
 * @return  处理后的数字
 */
export const floorKeepDecimals = (num, decimals = 2) => {
  const factor = Math.pow(10, decimals)
  const result = Math.floor(num * factor) / factor
  return Number(result.toFixed(decimals))
}

/**
 * 向上取整保留x位小数
 * @param   num	待处理数字
 * @param   decimals 需要保留的小数位
 * @return  处理后的数字
 */
export const ceilKeepDecimals = (num, decimals = 2) => {
  const factor = Math.pow(10, decimals)
  const result = Math.ceil(num * factor) / factor
  return Number(result.toFixed(decimals))
}