將數學運算從 反轉為-

我想在 Javascript 中轉換數學運算。例如，給定一個“-”，它應該被轉換為“ ”、“*”-“/”等等。

我當前的代碼是一個開關盒，執行起來真的很慢：

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);
            }

這個問題有更好/更快的解決方案嗎？

uj5u.com熱心網友回復：

性能可以忽略不計，但對于將一個事物映射到另一個事物的操作，從長遠來看，表驅動的方法通常更易于維護：

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

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

uj5u.com熱心網友回復：

我添加了一些背景關系來制作一個運行示例。

順便說一句，這里使用的方法是反轉規則的映射，替換了您在 switch 陳述句中使用的邏輯：

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>

標籤：javascript 功能 数学

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