Allow empty string with regex

Question

I'm trying to check if there's a number in a text input using regular expression. Here's the code:

var regex = /^[0-9]+$/;
if (myInput.val().match(regex)) {
    console.log("number");
} else {
    console.log("bad");
}

It works well, but if I add text, then backspace all the way, I get "bad". How can I make it log "good" when there isn't anything in the text input? I don't want to allow spaces, but I want to allow an empty input.

I tried:

var regex = /\s ^[0-9]+$/;

But then whatever I insert in the input, I always get "bad".

Try /^[0-9]*$/ and use RegExp#test instead of String#match — Tushar
– Tushar, Commented Dec 8, 2015 at 5:46
Why not just do two checks? if (!val.length || val.match(regex)) — epascarello
– epascarello, Commented Dec 8, 2015 at 5:48
@Tushar Can you explain about the RegExp#test and explain why it's better than what I have? — Horay
– Horay, Commented Dec 8, 2015 at 5:51
@epascarello I thought of that, but then what's the point of doing 2 checks when I can just do 1. — Horay
– Horay, Commented Dec 8, 2015 at 5:52
You said " if there's a number in a text". Do you mean you want to match positive on 1234, as well as on a1a,1ab12 and abd1? Not only on text which contains only numbers, but on number/letter as well? — yoko
– yoko, Commented Dec 8, 2015 at 6:09

yoko · Accepted Answer · 2015-12-08 17:04:25Z

5

This might fit , either you test for your Exp (^[a-zA-Z0-9]+$) or for an empty string (^$).

var regex = /(^$)|(^[a-zA-Z0-9]+$)/;
if (myInput.val().match(regex)) {
    console.log("number");
} else {
    console.log("bad");
}

edited Dec 8, 2015 at 17:04

answered Dec 8, 2015 at 6:02

yoko

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4 Comments

Horay Over a year ago

How does your answer differ from @gurvinder372's answer? Which one is recommended, and why?

yoko Over a year ago

In my RegEx I am trying first to check for an empty string, if this is not the case, i am checking for digits. Basically the same as gurvinder, but on the one hand i never feel comfortable with the * operator, on the other hand it might run faster, if you check for an empty string first, and only using the "bigger" one afterwards. Also, did you read my comment in your OP?

Horay Over a year ago

Is it bad to use * ?

yoko Over a year ago

imho greedy Operators are never a good thing. But since i am using +.. well, I did not say my solution was perfect. But since * catches even more than +, i tend to use it as less as possible.

gurvinder372 · Accepted Answer · 2015-12-08 06:19:54Z

1

try this (* in place of +)

var regex = /^[0-9]*$/;
if (myInput.val().test(regex)) {
    console.log("number");
} else {
    console.log("bad");
}

edited Dec 8, 2015 at 6:19

answered Dec 8, 2015 at 5:46

gurvinder372

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