How to copy case pattern when doing string replace?

Question

For example if a word is "Users" and the replacement is "utilisateurs", is there some kind of function that will allow me to conver the replacement string to the same level of capitals/non-capitals as the original word?

This is a final part of a major language translation using jquery, textnodes, exact and partial string matching.

Now I just want to make sure as the final and professional touch, is to make sure the case of the translated/replaced words, match the case of the original words/phrases.

I am not sure how I can apply this as a replace call.

I want this to be as a function

function CopyCase(original,new) {

    // copy the case of the original to the new
}

Only not sure how to do that.

Answer 1

Here's a function that will handle cases without internal capitalization:

function caseWord(word, upper) {
    return String.prototype[ upper ? "toUpperCase" : "toLowerCase"].apply(word[0]) + word.slice(1);
}
function caseReplace(s, fromWord, toWord) {
    return s.replace(caseWord(fromWord), caseWord(toWord))
            .replace(caseWord(fromWord, true), caseWord(toWord, true));
}

console.log(caseReplace("The users have joined the Users union.", "users", "utilisateurs"))
console.log(caseReplace("The lovers have joined the Lovers union.", "lovers", "amants"))

// The utilisateurs have joined the Utilisateurs union.
// The amants have joined the Amants union.