Replacement strings with dollar signs

Curriculum Help JavaScript
#1

Tell us what’s happening:
I don’t understand what the dollar sign does? Can someone give me another example because the example that is given doesn’t make any sense to me.
Why are we using a capture group when they are used to look for repeat substrings?

Your code so far


let str = "one two three";
let fixRegex = /(\w+)\s(\w+)\s(\w+)/; // Change this line
let replaceText = ""; // Change this line
let result = str.replace(fixRegex, replaceText);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36.

Challenge: Use Capture Groups to Search and Replace

Link to the challenge:

#2

The dollar sign$ in regex means the end or the beginning of a string. So it means to stop when the $ is in the end or to start from a particular letter if the $ is on the front.

#3

But then in the answer, it has you use
let replaceText="$3 $2 $1"
can you explain what that means in this code? How does the number ‘3’ translate to the string ‘three’?

#4

do you mean like this?

let first_last = "Bob Smith";
let r = /([a-z]+)\s([a-z]+)/i;
let last_first = first_last.replace(r, "$2, $1");
console.log(last_first); // Smith, Bob

the dollar sign plus number symbols are placeholders, and refer back to the capture groups, so $1 will refer to the first capture group, and $2 to the second capture group, they can be used to take parts of the original string and still keep them but maybe add something, or move them around

2 Likes
#5

Yes, that makes sense to me. Thanks!

#6

Do you know why we are using the \w instead of using the something such as [a-z] if we are searching through just strings?

#7

If you use \w you are typing less, and it includes all word characters (it’s equal to [a-zA-Z0-9_])
it depends on what you need to do. In the case of this challenge both \w and [a-z] give the same result so it doesn’t matter.

1 Like
#8

Coming back to the ‘+’ again… Why is it necessary to use the + with \w if we are just looking for strings of letters as opposed to multiple repeats of the strings?

#9

if you use [a-z] that is one letter, but if you want to capture one word, it is (or can be) more than one letter, so you use the + to say “match one or more letters, matching as much as possible”

#10

Can you help me clarify then, the difference between the “.” and +
I thought that the + was looking for multiple of the same thing and the . was just including whatever comes after the matched element.

#11

the . symbol will match a single character, it is a jolly, it will match anything, but still only one character.

the + is an other thing altogether, it will say that the last thing before it instead of being matched only one time, it can be matched once or more

so if you have /a/ it will just match a single “a”. if you have /a./ it will match a single “a” followed by any character, and if you have /a+/ it will match one or more "a"s.