How to make a simple calculator using HTML+CSS+JavaScript

JavaScript is an essential part of front-end development, because the realization of page functions cannot be separated from JS. As a front-end developer, can you use JavaScript to make a simple calculator? This article will tell you how to make a simple calculator using HTML, CSS, and JavaScript, and it can realize the functions of addition, subtraction, multiplication and division. It has certain reference value and interested friends can take a look.

Making a simple calculator requires a lot of CSS attributes, HTML tags and JavaScript knowledge. If you are unclear, you can refer to the relevant articles on the PHP Chinese website, or visit JavaScript video tutorial , hope it helps you.

Instance description: Use HTML and CSS to build a page, use JavaScript to implement the functions of addition, subtraction, multiplication and division. When you click to clear, the input box has no value. When you click "=", the calculation result is displayed. The specific code is as follows :

HTML part:

<div class="center">
   <h1>计算器</h1>   
   <form name="calculator">
    <input type="button" id="clear" class="btn other" value="C">
    <input type="text" id="display">
     <br>
    <input type="button" class="btn number" value="7" onclick="get(this.value);">
    <input type="button" class="btn number" value="8" onclick="get(this.value);">
    <input type="button" class="btn number" value="9" onclick="get(this.value);">
    <input type="button" class="btn operator" value="+" onclick="get(this.value);">
     <br>
    <input type="button" class="btn number" value="4" onclick="get(this.value);">
    <input type="button" class="btn number" value="5" onclick="get(this.value);">
    <input type="button" class="btn number" value="6" onclick="get(this.value);">
    <input type="button" class="btn operator" value="*" onclick="get(this.value);">
     <br>
    <input type="button" class="btn number" value="1" onclick="get(this.value);">
    <input type="button" class="btn number" value="2" onclick="get(this.value);">
    <input type="button" class="btn number" value="3" onclick="get(this.value);">
    <input type="button" class="btn operator" value="-" onclick="get(this.value);">
     <br>
    <input type="button" class="btn number" value="0" onclick="get(this.value);">
    <input type="button" class="btn operator" value="." onclick="get(this.value);">
    <input type="button" class="btn operator" value="/" onclick="get(this.value);">   
    <input type="button" class="btn other" value="=" onclick="calculates();">
   </form>
  </div>

CSS part:

* {
    border: none;
    font-family: 'Open Sans', sans-serif;
    margin: 0;
    padding: 0;
   }   
   .center {
    background-color: #fff;
    border-radius: 50%;
    height: 600px;
    margin: auto;
    width: 600px;
   }
   h1 {
    color: #495678;
    font-size: 30px; 
    margin-top: 20px;
    padding-top: 50px;
    display: block;
    text-align: center;
   }   
   form {
    background-color: #495678;
    margin: 40px auto;
    padding: 40px 0 30px 40px; 
    width: 280px;
   }
   .btn {
    outline: none;
    cursor: pointer;
    font-size: 20px;
    height: 45px;
    margin: 5px 0 5px 10px;
    width: 45px;
   }
   .btn:first-child {
    margin: 5px 0 5px 10px;
   }
   .btn, #display, form {
    border-radius: 25px;
   }
   #display {
    outline: none;
    background-color: #98d1dc;
    color: #dededc;
    font-size: 20px;
    height: 47px;
    text-align: right;
    width: 165px;
    padding-right: 10px;
    margin-left: 10px;
   }
   .number {
    background-color: #72778b;
    color: #dededc;
   }
   .number:active {
      -webkit-transform: translateY(2px);
      -ms-transform: translateY(2px);
      -moz-tranform: translateY(2px);
      transform: translateY(2px);
   }
   .operator {
    background-color: #dededc;
    color: #72778b;
   }
   .operator:active {
      -webkit-transform: translateY(2px);
      -ms-transform: translateY(2px);
      -moz-tranform: translateY(2px);
      transform: translateY(2px);
   }
   .other {
    background-color: #e3844c;
    color: #dededc;
   }
   .other:active {
      -webkit-transform: translateY(2px);
      -ms-transform: translateY(2px);
      -moz-tranform: translateY(2px);
      transform: translateY(2px);
   }

JavaScript part:

/* limpa o display */ 
  document.getElementById("clear").addEventListener("click", function() {
   document.getElementById("display").value = "";
  });
  /* recebe os valores */
  function get(value) {
   document.getElementById("display").value += value; 
  }   
  /* calcula */
  function calculates() {
   var result = 0;
   result = document.getElementById("display").value;
   document.getElementById("display").value = "";
   document.getElementById("display").value = eval(result);
  };

The effect is as shown in the figure:

The above has shared with you the code for making a simple calculator using HTML, CSS and JavaScript. It may be difficult for beginners. Don’t worry. After you learn the basic knowledge solidly, I believe that It’s easy for you to understand, I hope this article will be helpful to you!

【Recommended tutorials】

1. JavaScript Chinese Reference Manual
2. CSS3 Tutorial
3. bootstrap tutorial

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