Javascript with HTML if statement

Question

I am currently using JavaScript with HTML to create a number input, and once a number is input, an option from a select list tells whether to double the number or not. I feel I have done everything correctly, however, when I run my code and select yes to double, the output number is the number input and does not double. I am assuming my if statement is incorrect but I am not sure, I am new to JavaScript. Appreciate any feedback.

HTML

<body>
    <input id = 'number' name = '' value = '' class = ''>
    <select id = 'double' name = ''>
        <option value = 'Y'>YES</option>
        <option value = 'N'>NO</option>
    </select>
    <button id = 'go' class = ''>GO</button>
    <input id = 'result' name = '' value = '' class = ''>
    <script src = 'js/javascript 03.js'></script>
</body>

JavaScript

document.getElementById('go').onclick = function () {
    var number = document.getElementById('number').value;
    var double = document.getElementById('double').value;
    number = parseFloat(number);

    if (double == 'Y') {
        number * 2;
    };

    document.getElementById('result').value = number;
};

number * 2 does indeed double the number... but with no = in that line it doesn't get assigned to anything. — Niet the Dark Absol
– Niet the Dark Absol, Commented Oct 6, 2017 at 16:41
You need to reassign the variable number, use number = number * 2; — Titus
– Titus, Commented Oct 6, 2017 at 16:41
@NiettheDarkAbsol but if i assign number = number*2 that defeats the purpose of choosing yes to double and no to keep the number the same. it just doubles it every time — Astonishing
– Astonishing, Commented Oct 6, 2017 at 16:49
Spaces between attributes, = and values is invalid html, i'm not quite sure that it will even render properly. — Get Off My Lawn
– Get Off My Lawn, Commented Oct 6, 2017 at 18:22
@Astonishing Nooooo... because you're doing that inside the if(double == 'Y') check... — Niet the Dark Absol
– Niet the Dark Absol, Commented Oct 6, 2017 at 18:27

Salketer · Accepted Answer · 2017-10-06 16:42:54Z

1

number * 2; does not store the value anywhere. You should use one of the 2 cases here:

number *= 2;
number = number * 2;

answered Oct 6, 2017 at 16:42

Salketer

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1 Comment

Astonishing Over a year ago

but if i assign number = number*2 that defeats the purpose of choosing yes to double and no to keep the number the same. it just doubles it every time

nbkhope · Accepted Answer · 2017-10-06 16:45:13Z

0

As mentioned in the comments to your question, doing just number * 2 will evaluate to a value. But that value is not stored anywhere, so you need to put it back in its own variable:

number = number * 2;

answered Oct 6, 2017 at 16:45

nbkhope

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Comments

mk7644 · Accepted Answer · 2019-10-15 02:20:33Z

0

    int colCount=5;

    File fpath = new File("C:\\Users\\man.xls");
    FileInputStream file = new FileInputStream(fpath);

    if (fpath.exists()) {
        HSSFWorkbook wb = new HSSFWorkbook(file);
        int sCount =wb.getActiveSheetIndex();
        Sheet sh = wb.getSheetAt(sCount);

        int rwNum = sh.getLastRowNum();
        sh.createRow(rwNum+1);
        int rwNuafterr = sh.getLastRowNum();

        Row rw = sh.getRow(rwNuafterr);
        for (int j = 0; j <= colCount; j++) {
            rw.createCell(j);
            rw.getCell(j).setCellValue("char");
        }
        FileOutputStream outputStream = new FileOutputStream("C:\\Users\\man.xls");
        wb.write(outputStream);
    }

edited Oct 15, 2019 at 2:20

answered Mar 23, 2019 at 10:49

mk7644

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