brackets.js

const genBrackets = function(n) {
    const result = []

    if ( n > 0 ) {
        genBrackets.add(n, 0, "", result)
    }

    return result.join(" ")
}

genBrackets.add = function(left, right, buffer, result) {
    if ( !left && !right ) {
        result.push(buffer)
    }

    if ( left > 0 ) {
        genBrackets.add(left-1, right+1, buffer+"(", result)
    }

    if ( right > 0 ) {
        genBrackets.add(left, right-1, buffer+")", result)
    }
}

console.log(genBrackets(0)) // 
console.log(genBrackets(1)) // ()
console.log(genBrackets(2)) // (()) ()()
console.log(genBrackets(3)) // ((())) (()()) (())() ()(()) ()()()
console.log(genBrackets(4)) // (((()))) ((()())) ((())()) ((()))() (()(())) (()()()) (()())() (())(()) (())()() ()((())) ()(()()) ()(())() ()()(()) ()()()()