got a question about the start of string regex anchor tag ^.
I was trying to sanitize a string to check if it's a palindrome and found a solution to use regex but couldn't wrap my head around the explanations I found for the start of string anchor tag:
^ denotes that whatever expression that follows must match, starting from the beginning of the string.
Why then is there a difference between the two output below:
1)
let x = 'A man, a plan, a canal: Panama';
const re = new RegExp(/[^a-z]/, 'gi');
console.log(x.replace(re, '*'));
Output: A*man**a*plan**a*canal**Panama
VS.
2)
let x = 'A man, a plan, a canal: Panama';
const re = new RegExp(/[a-z]/, 'gi');
console.log(x.replace(re, '*'));
Output: * ***, * ****, * *****: ******
VS.
3)
let x = 'A man, a plan, a canal: Panama';
const re = new RegExp(/^[a-z]/, 'gi');
console.log(x.replace(re, '*'));
Output: * man, a plan, a canal: Panama
Please let me know if my explanation for each of the case above is off:
1) Confused about this one. If it matches a character class of [a-z] case insensitive + global find, with start of string anchor ^ denoting that it must match at the start of each string, should it not return all the words in the sentence? Since each word is a match of [a-z] insensitive characters that occurs at the start of each string per global find iteration?
(i.e.
Q: Why does it then when I call replace does it only targets the non alpha stuff? Should I in this case be treating ^ as inverting [a-z]?
2) This seems pretty straight forward, finds all occurrence of [a-z]and replaces them with the start. Inverse case of 1)??
3) Also confused about this one. I'm not sure how this is different from 1).
/^[a-z]/gi to me means: "starting at the start of the string being looked at, match all alpha characters, case insensitive. Repeat for global find".
Compared to:
1) /[^a-z]/gi to me means: "match all character class that starts each line with alpha character. case insensitive, repeat search for global find."
To mean they mean exactly the same @_@. Please let me know how my understanding is off for the above cases.
Your first expression [^a-z] matches anything other than an alphabetic, lower case letter, therefore that's why when you replace with * all the special characters such as whitespace, commas and colons are replaced.
Your second expression [a-z] matches any alphabetic, lower case letter, therefore the special characters mentioned are not replaced by *.
Your third expression ^[a-z] matches a alphabetic, lower case letter at the start of the string, therefore only the first letter is replaced by *.
For the first two expressions, the global flag g ensures that all characters that match the specified pattern, regardless of their position in the string, are replaced. For the third pattern however, since ^ anchors the pattern at the beginning of the string, only the first letter is replaced.
As you mentioned, the i flag ensures case insensitivity, so that all three patterns operate on both lower and upper case alphabetic letters, from a to z and A to Z.
The character ^ therefore has two meanings: