Why this Javascript RegExp is returning true?

Question

I need to validate alpha characters (in a request, node.js) and what i used was:

/[a-zA-Z]+/.test(input)

BUT when a value null was passed, then it was validated OK (regexp returns TRUE) example:

/[a-zA-Z]+/.test(null) // <--- this returns true :(

Somebody can explain me this? i need to avoid nulls, thanks!

no, i was testing null, not "null", please use chrome console and type this: /[a-zA-Z]+/.test(null) — mzalazar, Jul 18 '16 at 00:35
no, you were testing `"null"`; js converts it to a string for the test() method... — dandavis, Jul 18 '16 at 00:36

score 5 · Accepted Answer · answered Jul 18 '16 at 00:32

5

The test() method executes a search for a match between a regular expression and a specified string. Returns true or false

RegExp.prototype.test() converts parameters passed to a String

For example /\d/.test(0) would also return true, as expected, where 0 is a Number passed as parameter.

answered Jul 18 '16 at 00:32

guest271314

Ohh my god, thank you very much!! :) that helps a lot :D – mzalazar Jul 18 '16 at 00:36

score 2 · Answer 2 · answered Jul 18 '16 at 00:34

2

Because .test() coerces the parameter to a string, you are effectively testing against 'null' - which evaluates to true.

answered Jul 18 '16 at 00:34

Wayne Allen

2 Answers2