Some regular expressions I've been studying

Question

I've found these regex elsewhere:

myString.replace(/^.*\//, '');
myString.replace(/\..*?$/, '');

My question is:

• do ^ and ?$ make any sense here?

And my interpretation is that ^ isn't relevant, because we are using.* which means "anything".

The second one means replace from the . any character in lazy mode till the end of the string. Which is the same as nothing.

So I'd write them:

myString.replace(/.*\//, '');
myString.replace(/\..*/, '');

But I am not 100% sure as my Regex is quite basic. Ideas?

Answer 1

Indeed, in the first regular expression the ^ is not really needed. The effect is the same without it.

However, in the second regular expression there is a difference when you omit the ? and the $ , because . does not match newline characters (unless you add s as modifier).

See the different results:

 let myString = `.this is multiline`; console.log(myString.replace(/\..*?$/, '')); console.log(myString.replace(/\..*/, ''));

Answer 2

And my interpretation is that ^ isn't relevant, because we are using.* which means "anything".

Yep, that's the start of the string, but if you're wanting all of the string it has no relevance. Also, go here for a great regex playground.

do ^ and?$ make any sense here?

To answer the second question, for regex /\..*?$/ , the?$ does not make sense with * , b/cx* means 0 or more of x and x? means 0 or 1 (unless you intentionally wanted 0 or 1 of 0 or more, but doubt that). This is taken directly from the help sheet on regexr.com.