Best way to validate a string in js

Question

I need to make sure that my string is a number and for doing that, I was using isNaN function and everything was working but I got a problem when I typed in my input field '0e1'.

I was wondering what's the best way to check if my string is a number and without scientific notation

It's not really clear from your question if you **do** or **do not** want to match things like `0e1` — Paolo Moretti, Nov 19 '14 at 22:22

score 2 · Answer 1 · answered Nov 19 '14 at 22:30

Try using regex. Here are some examples. The result is null if no match was found.

alert("0e1".match(/^[-+]?[0-9]*\.?[0-9]+$/))    // null
alert("1".match(/^[-+]?[0-9]*\.?[0-9]+$/))      // 1
alert("-1".match(/^[-+]?[0-9]*\.?[0-9]+$/))     // -1
alert("1.0".match(/^[-+]?[0-9]*\.?[0-9]+$/))    // 1.0
alert("-1.5".match(/^[-+]?[0-9]*\.?[0-9]+$/))   // -1.5
alert("-1.5 4".match(/^[-+]?[0-9]*\.?[0-9]+$/)) // null

score 0 · Answer 2 · answered Nov 19 '14 at 22:29

0

If you want your input to only be an integer or float do this instead;

var input = '0e1';

if(!isNaN(input) && (parseInt(input, 10).toString() == input || parseFloat(input).toString() == input)){
    //This is a valid number
}

answered Nov 19 '14 at 22:29

Preston S

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score 0 · Answer 3 · answered Nov 19 '14 at 22:50

0

Actually, the method you are using is fine. You have one problem with your code:

isNaN() should be !isNaN(). Remember, isNaN() checks if the number is NotaNumber. `!isNaN() checks if it IS a number.

isNaN(0e1) should return false because 0e1 is a number! I know, it's kind of confusing.

!isNaN(0e1) will return TRUE because !isNan() checks if a value IS a number.

I hope this helps.

answered Nov 19 '14 at 22:50

Ian Hazzard

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The OP is trying to check if my string is a number **without scientific notation**. In addition `isNaN` will fail in some edge cases like `!isNaN('') === true`, this should be the correct way to implement an `IsNumeric` function: http://stackoverflow.com/a/1830844/63011 (but it's not what the OP is asking) – Paolo Moretti Nov 19 '14 at 22:56
I would disagree with you. It's hard to tell from the way the OP asked the question, but I think he DOES want to use scientific notation. Otherwise he wouldn't of mentioned it. – Ian Hazzard Nov 19 '14 at 23:02
quoting his words: *check if my string is a number and without scientific notation* – Paolo Moretti Nov 19 '14 at 23:03
His question has been edited since I posted my answer. – Ian Hazzard Nov 19 '14 at 23:09
@PaoloMoretti, quote from original question: *I was using isNaN function but it's not working maybe because it looks like scientific notation.* – Ian Hazzard Nov 19 '14 at 23:10
His question was edited before you posted your answer, but I agree that it's not clear :) – Paolo Moretti Nov 19 '14 at 23:17
@PaoloMoretti, yes I see that, but I wrote it before and forgot to hit submit. – Ian Hazzard Nov 19 '14 at 23:18

score 0 · Answer 4 · answered Nov 19 '14 at 22:59

isNaN() function determines whether a value is an illegal number, so if it is not a number. The good thing about isNaN function is, that is suportet by all browsers (ch, ie, ff, op, sf).

function myFunction() {
    var a = isNaN(123) + "<br>";
    var b = isNaN(-1.23) + "<br>";
    var c = isNaN(123-456) + "<br>";
    var d = isNaN("Hello") + "<br>";
    var e = isNaN("2014/11/19") + "<br>";

    var result = a + b + c + d + e;
    document.getElementById("test").innerHTML = result;
}

So result would be: If value is a number return "False" if is not a number return "True".

You can test it on JsFiddle: isNaN()

Best way to validate a string in js

4 Answers4