When comparing MongoDB to Javascript, the $regex matching pattern yields varied results

Question

When comparing MongoDB to Javascript, the $regex matching pattern yields varied results

Currently, I am implementing the following $regex pattern in a mongo query:

{domain: {$regex: '^(.+\.)?youtube.com$'}}

I anticipate that it will match youtube.com as well as sub.youtube.com.

However, the issue I have encountered is that it also matches values like justyoutube.com.

Interestingly, in JavaScript, the match does not occur:

console.log(/^(.+\.)?youtube.com$/.test('justyoutube.com'));
// This returns `false` as expected.

Do you have any suggestions on improving this functionality? Is the problem related to my regex itself, or is it due to the regex library utilized by MongoDB?

Update: I have noticed that utilizing /pattern/ instead of 'pattern' yields the desired outcome. However, I am still interested in finding a solution using quotation marks for easier debugging in MongoDB Compass.

javascript regex mongodb

Answer 1

Answer №1

It seems like the backslash in the string you're passing is working as an escape character within the string itself, rather than being included in the actual regular expression. One way to handle this is to double the backslash to effectively 'escape the escape':

const unescaped = new RegExp('^(.+\.)?youtube.com$')
const escaped = new RegExp('^(.+\\.)?youtube.com$')

console.log(unescaped.test('justyoutube.com'));
console.log(escaped.test('justyoutube.com'));

console.log(unescaped.test('sub.youtube.com'));
console.log(escaped.test('sub.youtube.com'));

// Another approach is to use a template literal, which interprets all characters literally:

const withBacktick = new RegExp(`^(.+\.)?youtube.com$`);
console.log(withBacktick.test('sub.youtube.com'));
console.log(withBacktick.test('justyoutube.com'));

Answer 2

It seems like the backslash in the string you're passing is working as an escape character within the string itself, rather than being included in the actual regular expression. One way to handle this is to double the backslash to effectively 'escape the escape':

const unescaped = new RegExp('^(.+\.)?youtube.com$')
const escaped = new RegExp('^(.+\\.)?youtube.com$')

console.log(unescaped.test('justyoutube.com'));
console.log(escaped.test('justyoutube.com'));

console.log(unescaped.test('sub.youtube.com'));
console.log(escaped.test('sub.youtube.com'));

// Another approach is to use a template literal, which interprets all characters literally:

const withBacktick = new RegExp(`^(.+\.)?youtube.com$`);
console.log(withBacktick.test('sub.youtube.com'));
console.log(withBacktick.test('justyoutube.com'));

When comparing MongoDB to Javascript, the $regex matching pattern yields varied results

Answer №1

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