Input valueAsNumber

By  on  

Every once in a while I learn about a JavaScript property that I wish I had known about years earlier -- valueAsNumber is one of them. The valueAsNumber provides the value of an input[type=number] as a Number type, instead of the traditional string representation when you get the value:

/*
 Assuming an <input type="number" value="1.234" />
*/

// BAD: Get the value and convert the number
input.value // "1.234"
const numberValue = parseFloat(input.value, 10);

// GOOD: Use valueAsNumber
input.valueAsNumber // 1.234

This property allows us to avoid parseInt/parseFloat, but one gotcha with valueAsNumber is that it will return NaN if the input is empty.

Thank you to Steve Sewell for making me aware of valueAsNumber!

Recent Features

  • By
    9 Mind-Blowing WebGL Demos

    As much as developers now loathe Flash, we're still playing a bit of catch up to natively duplicate the animation capabilities that Adobe's old technology provided us.  Of course we have canvas, an awesome technology, one which I highlighted 9 mind-blowing demos.  Another technology available...

  • By
    Responsive and Infinitely Scalable JS Animations

    Back in late 2012 it was not easy to find open source projects using requestAnimationFrame() - this is the hook that allows Javascript code to synchronize with a web browser's native paint loop. Animations using this method can run at 60 fps and deliver fantastic...

Incredible Demos

  • By
    Rotate Elements with CSS Transformations

    I've gone on a million rants about the lack of progress with CSS and how I'm happy that both JavaScript and browser-specific CSS have tried to push web design forward. One of those browser-specific CSS properties we love is CSS transformations. CSS transformations...

  • By
    HTML5 Context Menus

    One of the hidden gems within the HTML5 spec is context menus. The HTML5 context menu spec allows developers to create custom context menus for given blocks within simple menu and menuitem elements. The menu information lives right within the page so...

Discussion

  1. Martin

    Great tip! Is there anything wrong with parseInt / parseFloat, apart from the extra line of code? (you labeled it “BAD”)

    • Kyryl

      Depending on lang, decimal separator can be comma. So, parseFloat('0,01'); will return 0 instead of 0.01.

  2. yann

    Leaving this here hoping it saves some time I wish I had saved to some other person looking for an answer…

    If you’re using this on an html input, maybe with angular… it works great, but you NEED to add the 'type="number"' to your input or it will keep giving u NaN no matter what’s in the input box.

    The reason ?
    for some reason that I am not looking up at this time, valueAsNumber does NOT work on String types, but the default type of an html input is String.

  3. Bonjour,

    parseFloat(string, 10) vs Number(string)

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!