Write a simple calculator using JavaScript

The effect is as follows:

Reference Program:

<!DOCTYPE html>

<html lang="en">



<head>

    <meta charset="UTF-8">

    <meta http-equiv="X-UA-Compatible" content="IE=edge">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <title>Analog Calculator</title>

    <style>

        button {

            width: 39px;

            height: 30px;

            background-color: rgb(102, 240, 102);

        }

        button:hover {

            background-color: black;

            color: rgb(255, 249, 237);

        }



        button:active {

            background-color: rgb(79, 72, 72);

            color: white;

        }

        table{

            background: rgb(192, 248, 109);

        }

    </style>

</head>



<body>

    <div>

        <table border="1px">

            <tr style="text-align: center;">

                <td colspan="4">

                    <input type="text" id="result" >

                </td>

            </tr>

            <tr>

                <td><button id="le" onclick="getChar('(')">(</button></td>

                <td><button id="rg" onclick="getChar(')')">)</button></td>

                <td><button id="baifen" onclick="getChar('%')">%</button></td>

                <td><button id="C" onclick="clear1()">C</button></td>

            </tr>

            <tr>

                <td><button id="seven" onclick="getChar('7')">7</button></td>

                <td><button id="eight" onclick="getChar('8')">8</button></td>

                <td><button id="nine" onclick="getChar('9')">9</button></td>

                <td><button id="divi" onclick="getChar('/')">/</button></td>

            </tr>

            <tr>

                <td><button id="four" onclick="getChar('4')">4</button></td>

                <td><button id="five" onclick="getChar('5')">5</button></td>

                <td><button id="six" onclick="getChar('6')">6</button></td>

                <td><button id="mul" onclick="getChar('*')">*</button></td>

            </tr>

            <tr>

                <td><button id="one" onclick="getChar('1')">1</button></td>

                <td><button id="two" onclick="getChar('2')">2</button></td>

                <td><button id="three" onclick="getChar('3')">3</button></td>

                <td><button id="dec" onclick="getChar('-')">-</button></td>

            </tr>

            <tr>

                <td><button id="zero" onclick="getChar('0')">0</button></td>

                <td><button id="point" onclick="getChar('.')">.</button></td>

                <td><button id="=" onclick="getResult()">=</button></td>

                <td><button id="add" onclick="getChar('+')">+</button></td>

            </tr>

        </table>

    </div>

</body>

<script>

    // Click the button to return the button value function getChar(btnid) {

        var btns = document.getElementsByTagName("button")

        switch (btnid) {

            case '+':

                setNum('+')

                break;

            case '.':

                setNum('.')

                break;

            case '=':

                setNum('=')

                break;

            case '0':

                setNum('0')

                break;

            case '1':

                setNum('1')

                break;

            case '2':

                setNum('2')

                break;

            case '3':

                setNum('3')

                break;

            case '-':

                setNum('-')

                break;

            case '4':

                setNum('4')

                break;

            case '5':

                setNum('5')

                break;

            case '6':

                setNum('6')

                break;

            case '7':

                setNum('7')

                break;

            case '8':

                setNum('8')

                break;

            case '9':

                setNum('9')

                break;

            case '/':

                setNum('/')

                break;

            case '*':

                setNum('*')

                break;

            case '(':

                setNum('(')

                break;

            case ')':

                setNum(')')

                break;

            case '%':

                setNum('%')

                break;

            default:

                break;

        }

    }

    // Clear the display function clear1() {

        document.getElementById("result").value = ""

    }

    // Display the value on the display function setNum(charCode) {

        var origin = document.getElementById('result');

        origin.value += charCode;

        origin.innerText = origin.value;

    }

    //Calculation result function getResult(){

        var res = eval(document.getElementById("result").value);

        // Append '='

        setNum('=');

        // Append result setNum(res)

    }

</script>

</html>

Note: When doing calculations, you can directly use the eval function. We don’t have to manually write the calculation logic of addition, subtraction, multiplication and division, which greatly simplifies development.

For example:

var num = eval('3+3')

The result of the operation is num=6

Eval function usage:

Syntax: eval (parameter), the parameter is a js expression, a string, which can contain variables and properties of existing objects

Return value:

Parameter Type	Return Value
Integer or function	Integer or function
String (and expression)	The result of running the string expression
String (a statement or a statement block)	Executes the statement block and returns undefined

This is the end of this article about using JavaScript to write a simple calculator. For more information about using JavaScript to write a simple calculator, please search for previous articles on 123WORDPRESS.COM or continue to browse the following related articles. I hope you will support 123WORDPRESS.COM in the future!

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