Regex unexpected result

Question

I am trying to check if the user input contains only 0 or 1 with Regex? But It also accepts different values.

inputChange = (e) => {
    console.log(/(^$)|[0,1]*/g.test(e.target.value));
};

The method above returns true for a string '222' but when I use online Regex checker it says that my Regex is correct.

simply with `| => AND` operator `0|1` https://regex101.com/r/5szLXO/2 — prasanth, Mar 15 '19 at 02:13

Code Maniac · Accepted Answer · 2019-03-15T02:26:02.953

1

Why it is matching other values too ?

Well [0,1]* here * means match zero or more time so in case of values other than 0 and 1 it still matches but zero time

So you can change * to +

/(?:^$)|^[01]+$/
    |     |__________  Matches string with only zero and one
    |     
    |________________  Match empty strings. ( Non capturing group)

console.log(/(?:^$)|^[01]+$/.test('222'))
console.log(/(?:^$)|^[01]+$/.test(''))
console.log(/(?:^$)|^[01]+$/.test('1111111 111111'))  // fails because there's a space
console.log(/(?:^$)|^[01]+$/.test('010101'))

On side note:- You should not use g flag with test. read here why-does-a-regexp-with-global-flag-give-wrong-results

edited Mar 15 '19 at 02:26

answered Mar 15 '19 at 02:20

Code Maniac

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shouldn't 3rd case be returned true? – Bhojendra Rauniyar Mar 15 '19 at 02:24
@BhojendraRauniyar if you see carefully there's a space between values – Code Maniac Mar 15 '19 at 02:24
that's what i'm not able to know what exactly OP wants. because empty string returns true, so OP might want this case to return true. – Bhojendra Rauniyar Mar 15 '19 at 02:25
1

@BhojendraRauniyar i guess OP is checking some input field which takes number as input. i guess some sort of `phone number without country code` or `quantity` something – Code Maniac Mar 15 '19 at 02:28
Yes actually I want exactly the third case to return true but I modified your answer to /(?:^$)|^[01' ']+$/! Thanks everyone for the help. – Zotov Mar 15 '19 at 03:00
1

@Zotov you don't need `'` this, you can simply use `^[01 ]$` – Code Maniac Mar 15 '19 at 16:27

Regex unexpected result

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