simplify a string excluding an array

November 22, 2022

I want to remove every extra spaces, signs, and lowercase ( in another words I want to simplify) the string with a function. The following function does this perfectly:

console.log(simplify('   The     very optiMal! FUNCTION, {here] ...'));

function simplify(string) {
    return string.toLowerCase().replace(/[^A-Za-z0-9'_]+/g, " ").trim();
}

But the issue is I want to exclude an array of signs not to be removed from the string:

const signs = ['!!', '?!', '!?', '...', '..', '.', '?', '؟!', '!؟', '!', '؟', ':'];

So if the is any of the above signs in the string it should be intact and not be removed.

How would you do this?

>Solution :

You can use

const signs = ['!!', '?!', '!?', '...', '..', '.', '?', '؟!', '!؟', '!', '؟', ':'];
const exclusion = signs.map(x => x.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&')).join("|");
const regex = new RegExp("(" + exclusion + ")|(?:(?!" + exclusion +")[^A-Za-z0-9'_])+", "g");

function simplify(string) {
    return string.toLowerCase().replace(regex, (x,y) => y || " ").trim();
}

console.log(simplify('   The     very optiMal! FUNCTION, {here] ...'));

Details:

(<exclusion>) – Group 1 with exclusion patterns
| – or
(?:(?!<exclusion>)[^A-Za-z0-9'_])+ – a char other than an ASCII alphanumeric, underscore or ' chars, one or more but as many as possible occurrences, that does not start any of the exclusion patterns (since some of them are multi-character they cannot be simply included to the original negated character class).

The replacement is the Group 1 contents if Group 1 matches, else, the replacement is a space.

Another way to approach the issue – in case you want to always have a space separating each substring – is to use a reverse approach: match what you need and then join with a space:

const signs = ['!!', '?!', '!?', '...', '..', '.', '?', '؟!', '!؟', '!', '؟', ':'];
const exclusion = signs.map(x => x.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&')).join("|");
const regex = new RegExp(exclusion + "|[A-Za-z0-9'_]+", "g");

function simplify(string) {
    return string.toLowerCase().match(regex).join(" ");
}

console.log(simplify('this is...'));