Regex for MongoDB ObjectID

Question

With reference to this SO question, I have a scenario where I only need to match a hex string with a-f included. All else should not match. Example:

checkForHexRegExp.test("112345679065574883030833"); // => false checkForHexRegExp.test("FFFFFFFFFFFFFFFFFFFFFFFF"); // => false checkForHexRegExp.test("45cbc4a0e4123f6920000002"); // => true 

My use case is that I am working with a set of hex strings and would like to only validate as true those that are mongodb objectIDs.

Answer 1

You can use following regular expression but it will not quite work

checkForHexRegExp = /^(?=[a-f\d]{24}$)(\d+[a-f]|[a-f]+\d)/i 

Example:

> checkForHexRegExp.test("112345679065574883030833") false > checkForHexRegExp.test("FFFFFFFFFFFFFFFFFFFFFFFF") false > checkForHexRegExp.test("45cbc4a0e4123f6920000002") true 

But, as I commented, 112345679065574883030833, FFFFFFFFFFFFFFFFFFFFFFFF are also valid hexadecimal representations.

You should use /^[a-f\d]{24}$/i because it passes all the above tests