Input valueAsNumber

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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!

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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)

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