将数学运算从 + 反转为 -

Question

我想转换 Javascript 中的数学运算。例如给定一个“-”，它应该被转换为一个“+”，“*”-“/”等等。

我现在的代码是switch case，执行起来真的很慢：

if (contents.className == "buttonfunction") {
                if (invert == true) {
                    switch (contents.innerHTML) {
                        case "+":
                            contents.innerHTML = "-";
                            break;
                        case "-":
                            contents.innerHTML = "+";
                            break;
                        case "*":
                            contents.innerHTML = "/";
                            break;
                        case "/":
                            contents.innerHTML = "*";
                            break;
                    }
                } 
                document.body.appendChild(contents);
            }

这个问题有better/faster解决方案吗？

Answer 1

性能可以忽略不计，但对于将一个事物映射到另一个事物的操作，table-driven 方法在较长的运行中通常更易于维护：

const inverseOperations = {
 '+': '-',
 '-': '+',
 '/': '*',
 '*': '/',
};

if (contents.className == "buttonfunction") {
  const operation = contents.innerHTML
  if (invert == true && inverseOperations[operation]) {
    contents.innerHTML = inverseOperations[operation];
  }
  document.body.appendChild(contents);
}

Answer 2

我添加了一些上下文来制作一个运行示例。

顺便说一句，这里使用的方法是反转规则映射，替换您在 switch 语句中使用的逻辑：

let invert = true;

//granular map of pairs declaring the inverse of each operator
//it could be declared inline here but it could be also fed with the addInversionInMap
let inverted = {}; //{ '+' : '-', '-' : '+', '*' : '/', '/' : '*'}

addInversionInMap('+','-');
addInversionInMap('*','/');
//feeds the inverted map without repeating the both the sides in declaration
function addInversionInMap(op, opInverted){  
  inverted[op] = opInverted;
  inverted[opInverted] = op;  
}

//on document ready adds the click handler to every .buttonfunction elements
document.addEventListener("DOMContentLoaded", function() {
  addClickHandlerToButtonsFunction();
});

//adds the handler for click event on .buttonfunction
function addClickHandlerToButtonsFunction(){
  let btns = Object.values(document.getElementsByClassName('buttonfunction'));
  for(let btn of btns){
    btn.addEventListener('click', invertValue);
   }
}

//return the inverted operator based on the inverted map
//(or return the operator as is if there's no way to invert)
function getInvert(operator){
  if(inverted.hasOwnProperty(operator))
    return inverted[operator];
  else
    return operator;
}

//inverts the value of the element whose id is declared in the data-target attribvute
//of the button that triggered the click event (such element should be input type text)
function invertValue(){
  let contents = window.event.target;
  if (contents.className == "buttonfunction") {
    if (invert == true) {   
      let targetId = contents.getAttribute('data-target');
      let target = document.getElementById(targetId);
      //I'm using value so I expect the element to be input type text
      target.value = getInvert(target.value);
    }    
  }
}

button.buttonfunction{
  cursor: pointer;
}

<input id="input" type="text"></input>
<button type="button" class="buttonfunction" data-target="input">Invert</button>

将数学运算从 + 反转为 -

Inverting a math operation from + to -

javascript

math

function