Javascript regex to find a pattern in a string, excluding a possible preceding word match

Question

There is a string of writing/text in a variable:

var copypaste, replaced;
var verbdb = ["keep","know","enjoy"];
var arrayLength = verbdb.length;

for (var i = 0; i < arrayLength; i++) {
    copypaste = "One of the reasons first_name keep waking up at night, is blah blah blah. Try this, let first_name know and see blah blah blah. Remember that first_name enjoy being challenged and blah blah blah.";

    replaced = copypaste.replace(RegExp("[^let]? first_name " + verbdb[i] + "(\s|\.)","g")," first_name " + verbdb[i] + "_object_s\$1");
}

---

What I am seeking to get from the replaced variable is to exclude ONLY when first_name is preceded by the word let .

"One of the reasons first_name keep_object_s waking up at night, is blah blah blah. Try this, let first_name know and see blah blah blah. Remember that first_name enjoy_object_s being challenged and blah blah blah.";

---

So in this example:

1. the first pattern MATCHES (keep) and is replaced with _object_s added in,
2. the second pattern does NOT match (know) because of the word "let", so no replacement
3. the third pattern MATCHES (enjoy) and is replaced with _object_s added in.

Answer 1

You can try this :

(?:\b)(?!let)(?=\w+\sfirst_name\s+(know|keep|enjoy))(\w+ \w+)\s+(\w+)

Explanation

 const regex = /(?:\\b)(?!let)(?=\\w+\\sfirst_name\\s+(know|keep|enjoy))(\\w+ \\w+)\\s+(\\w+)/g; const str = `One of the reasons first_name keep waking up at night, is blah blah blah. Try this, let first_name know and see blah blah blah. Remember that first_name enjoy being challenged and blah blah blah`; const subst = `$2 _object_s`; const result = str.replace(regex, subst); console.log(result);