如何让等号在JavaScript中重复计算？

Question

简要说明：我正在尝试使用 html 和 JavaScript 制作一个基本计算器。到目前为止，我已经使用数字、运算符、小数和等号键（按钮）成功完成了计算器的所有基本功能。

问题：我试图通过在操作完成后多次按等号来实现它，它将执行最后一个操作。比如下面的例子：

运算：5+6-3

答案（等号按一次）：8

按两次等号：8-3 = 5（我的代码中没有出现这种情况，似乎无法找出原因）

这种情况下的最后一个操作是“-3”

代码如下，我使用了大部分函数和不会导致问题的代码位，因为我的代码大约有 200 行。（以下代码约80行）

代码：

var keys = document.querySelectorAll('#calculator span');
var operators = ['+', '-', 'x', '÷'];
var input;
var inputValue;
var buttonValue;
var equalOnce = false;
var decimalAdd = false;
var lastOperation;

readIn(keys, input, inputValue,buttonValue);

function readIn(keys, input, inputValue, key) {
  for(var i = 0; i < keys.length; i++) {
    keys[i].onclick = function(e) {
      input = document.querySelector('.screen');
      inputValue = input.innerHTML;
      key = this.innerHTML;
      keyPressed(key, inputValue, input);
    }
  }
}

//clears screen and input
function clearScreen(input){}

 //calculates all math functions within the equation.
function evalulated(lastCharacter, equations, operator, input){
      //replaces x with * and ÷ with /
      equations = equations.replace(/x/g, '*').replace(/÷/g, '/');
      //checks last character and removes if its an decimal or operator
      if(operator.indexOf(lastCharacter) > -1 || lastCharacter == '.')
        equations = equations.replace(/.$/, '');
      if(equations){
        input.innerHTML = eval(equations);
      }
      return;
    }

//finds the last operator and take the operator and the last digits/number used with the operrator and save it into lastOperation
function findLastEquation(equation, lastOperation){
  var plusLastIndex = equation.lastIndexOf('+');
  var subLastIndex = equation.lastIndexOf('-');
  var divideLastIndex = equation.lastIndexOf('÷');
  var multipleLastIndex = equation.lastIndexOf('x');

  if(plusLastIndex > subLastIndex && plusLastIndex > divideLastIndex  && plusLastIndex > multipleLastIndex){
    lastOperation = equation.slice(plusLastIndex, equation.length);
  }else if(subLastIndex > plusLastIndex && subLastIndex > divideLastIndex  && subLastIndex > multipleLastIndex){
    lastOperation = equation.slice(subLastIndex, equation.length);
  } else if(divideLastIndex > plusLastIndex && divideLastIndex > subLastIndex  && divideLastIndex > multipleLastIndex){
    lastOperation = equation.slice(divideLastIndex, equation.length);
  } else if(multipleLastIndex > plusLastIndex && multipleLastIndex > subLastIndex  && multipleLastIndex > divideLastIndex){
    lastOperation = equation.slice(multipleLastIndex, equation.length);
  }else{
    lastOperation = 0;
  }
  return lastOperation;
}

function keyPressed(key, inputValue, input) {
  var equation;
  var lastChar;
  var newEquation;

  if(key == 'C') {
    clearScreen(input);
  }
  else if(key == '=') {
    if(equalOnce == false) {
      equalOnce = true;
      equation = inputValue;
      lastOperation = findLastEquation(equation, lastOperation);
    }else {
      equation = equation.concat(lastOperation);
      alert(equation);
    }
    lastChar = equation[equation.length - 1];
    evalulated(lastChar, equation, operators, input);

    decimalAdd = false;
  }
  else if(operators.indexOf(key) > -1) {
    lastChar = inputValue[inputValue.length - 1]; 
    if(operators.indexOf(lastChar) > -1 && inputValue.length > 1) {}
    equalOnce = false;
  }
  //adds a decimal to input, adds a '0.' if no integer was before it
  else if(key == '.' && equalOnce == false) {
    if(decimalAdd == false) {}
      input.innerHTML += key;
      decimalAdd = true;
    }
    equalOnce = false;
  }
  else {          
    if(equalOnce == true){
      clearScreen(input);
    }
    if(key == '.'){}
    input.innerHTML += key;
  }

}

任何帮助或建议都将非常有用！提前致谢！

Answer 1

我忘了写声明：

equation = inputValue;

在 if(key == '='){} 中的 if else 语句之外现在工作正常。

如何让等号在JavaScript中重复计算？

How to make equal sign do repetitive calculation in JavaScript?

html

javascript

calculator