regex pattern test evaluating as true for everything

Question

I have the following regex named 'pattern' that I am testing to try to restrict an input to only numbers. Why are both pattern.test("a") and pattern.test("1") returning true?

const pattern = /^[a-zA-Z0-9]*$/;
if (!pattern.test(event.target.value)) {
    event.target.value = event.target.value.replace(/[^a-zA-Z0-9]/g, "");
}

What is `event.target.value` string, number? – onetwo12 Sep 02 '20 at 20:01 — onetwo12, Sep 02 '20 at 20:01
`/^[a-zA-Z0-9]*$/` matches an alphanumeric only string. – Wiktor Stribiżew Sep 02 '20 at 20:02 — Wiktor Stribiżew, Sep 02 '20 at 20:02

Brenden · Accepted Answer · 2020-09-02T20:09:23.860

2

Your expressions /^[a-zA-Z0-9]*$/ matches character ranges a-z, A-Z, 0-9. This will match any alphanumeric character. Adding the * means any number of times including zero. Meaning an empty string will also match.

If you want to match numeric and empty string only use /^[0-9]*$/.

If you want to match numeric only use /^[0-9]+$/.

edited Sep 02 '20 at 20:09

answered Sep 02 '20 at 20:02

Brenden

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...where `''` represents an empty string... not the character `"`. I had to do a double-take. – spender Sep 02 '20 at 20:04
1

edited that. That was confusing. – Brenden Sep 02 '20 at 20:05

regex pattern test evaluating as true for everything

1 Answers1