js浮点运算式

结果

calc('0.23*-0.03+(4*0.2)') =>0.7931

代码

//加|减|乘|除 浮点运算 
const floatMulti = (a, b) => {
  let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
  m = (s1l ? s1l.length : 0) + (s2l ? s2l.length : 0)
  return Number(s1.replace('.', '')) * Number(s2.replace('.', '')) / Math.pow(10, m)
}
const floatSub = (a, b) => {
  let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
  m = Math.max((s1l ? s1l.length : 0) ,(s2l ? s2l.length : 0))
  return(Number(s1)*Math.pow(10, m) - Number(s2)*Math.pow(10, m)) / Math.pow(10, m)
}
const floatAdd = (a, b) => {
  let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
  m = Math.max((s1l ? s1l.length : 0) ,(s2l ? s2l.length : 0))
  return (Number(s1)*Math.pow(10, m) + Number(s2)*Math.pow(10, m)) / Math.pow(10, m)
}
const floatDev = (a, b) => {
  let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
  m = (s1l ? s1l.length : 0) + (s2l ? s2l.length : 0)
  return (Number(s1.replace('.', '')) / Number(s2.replace('.', ''))) / Math.pow(10, m)
}
/*
* 浮点运算式
* */
export const calc = (() => {
  //一般的算数表达式即为中缀表达式
  // let str = "1+((2 + 3 ) * 4 ) - 5 ";

  //运算符权重
  const sdw = { '+': 1, '-': 1, '*': 2, '/': 2 };

  //循环安全数
  let saveCircle = 137;

  /**
   *判断是 运算符|操作数|括号
   * 【-】字符前面有任何其他运算符则本身被当作数字一部分
   *@return 1:操作数 2:括号 0:运算符
   */
  const typeChk = (d) => /^-*[\.\d]+$/.test(d) ? 1 : (/[\(\)]/.test(d) ? 2 : 0)
  /*
  * 操作符操作方法
  * */
  const handle = { '+': floatAdd, '-': floatSub, '*': floatMulti, '/': floatDev }
  /**
   * 处理输入
   * 1) 替换中英括号
   * 2) 去除空格
   * 3) 小数点前后非数字，则去除
   * 3) 小数点之前为空,后面为数字则默认前面添加0
   * 4) 返回字符分割
   */
  const dealStr = (str) => str
    //替换左右括号
    .replace(/（/, '(')
    .replace(/）/, ')')
    //替换空字符
    .replace(/[^\d\.\(\)\+\*\/-]/g, '')
    //替换-
    // .replace(/(\d)-/g,'$1+-')
    // .replace(/--/g,'+')
    // .replace(/-\(/g,'-1*(')
    // .replace(/-/g,'+-1*')
    .match(/(((?<=[^\d])-[\.\d]+)+)|(^-[\.\d]+)|([\d\.]+)|([\(\)\+\*\/-])/g)

  //中缀表达式转前缀表达式并计算
  return (str) => {
    let operand = [];//操作数栈
    let operator = [];//操作符栈
    //去空格(主要是避免数字被空格拆分),分割成数组
    let arr = dealStr(str);
    // log(arr)
    //按照规则入栈
    let type;
    for (let i = arr.length - 1, curr; (curr = arr[i]) != null; i--) {
      type = typeChk(curr);
      if (type === 1) {
        operand.push(+curr)
      } else if (type === 0) {
        let si = 0, stackTop;
        while (true && si++ < saveCircle) {
          stackTop = operator[operator.length - 1];
          if (stackTop == null || stackTop === ')') {
            operator.push(curr);
            break;
          } else if (sdw[curr] >= sdw[stackTop]) {
            operator.push(curr);
            break;
          } else {
            operand.push(operator.pop())
          }
        }
      } else {
        if (curr === ')') {
          operator.push(curr)
        }else{
          let s, si = 0;
          while (s !== ')' && si++ < saveCircle) {
            s = operator.pop();
            if (s === ')') break
            operand.push(s)
          }
        }
      }
    }
    //将操作符栈中剩下的弹出压入操作数栈
    // operand = [...operand, ...operator.reverse()];// num => ["5", "4", "3", "2", "+", "×", "1", "+", "-"]
    //"1+((2 + 3 ) × 4 ) - 5 "
    let prevStack = [...operator, ...operand.reverse()];// ["-", "+", "1", "×", "+", "2", "3", "4", "5"]

    //计算
    let resultStack = [], left, right;
    for (let i = prevStack.length - 1, curr; (curr = prevStack[i]) != null; i--) {
      if (typeChk(curr)) {
        //是操作数
        resultStack.push(curr)
      } else {
        //是操作符
        left = resultStack.pop();
        right = resultStack.pop();
        // console.log(left,right,curr)
        resultStack.push(handle[curr](left, right))
      }
    }
    // log(prevStack);
    //log(resultStack);
    return resultStack.length != 1 ? '表达式有误' : resultStack[0]
  }
})()