Restrict action of toLowerCase to part of a string?

Question

I want to convert most of a string to lower case, except for those characters inside of brackets. After converting everything outside the brackets to lower case, I then want to remove the brackets. So giving {H}ell{o} World as input should give Hello world as output. Removing the brackets is simple, but is there a way to selectively make everything outside the brackets lower case with regular expressions? If there's no simple regex solution, what's the easiest way to do this in javascript?

Answer 1

You can try this:

var str='{H}ell{o} World';

str = str.replace(/{([^}]*)}|[^{]+/g, function (m,p1) {
    return (p1)? p1 : m.toLowerCase();} );

console.log(str);

The pattern match:

{([^}]*)}  # all that is between curly brackets
           # and put the content in the capture group 1

|          # OR

[^{]+      # anything until the regex engine meet a {
           # since the character class is all characters but {

the callback function has two arguments:

m the complete match

p1 the first capturing group

it returns p1 if p1 is not empty else the whole match m in lowercase.

Details:

"{H}"    p1 contains H (first part of the alternation)
         p1 is return as it. Note that since the curly brackets are
         not captured, they are not in the result. -->"H"

"ell"    (second part of the alternation) p1 is empty, the full match 
         is returned in lowercase -->"ell"

"{o}"    (first part) -->"o"

" World" (second part) -->" world"