Basically a function which takes a string and gives back an array of all consisted words, takes numbers and underscores into account

GetWordsFromString.js

//
// Made by Bob Walter in 2k18
// Version 1.2.0
//


// ––– INPUT ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– //

// input string
let str = "8fOo Bar8 fOo8bar fOo-Bar fOo_Bar 8.8 888 ,_?!";


// ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– //

// regexps to filter words
const r1 = new RegExp(/[^\w]/,'g');
const r2 = new RegExp(/\b_|\b\d+(\s|$)/,'g');

// extending RegExp class, replaces input matches with spaces
class replaceWithSpaces extends RegExp {
  [Symbol.replace](str) {
    return RegExp.prototype[Symbol.replace].call(this, str, ' ');
  }
}

// extending RegExp class, splits string at input and returns map of betweenies
class makeMap extends RegExp {
  [Symbol.split](str, limit) {
    var result = RegExp.prototype[Symbol.split].call(this, str, limit);
    return result.map(x => x);
  }
}

// extending Array class with function, removes input element from array and fills with remainings
Array.prototype.remove = function(from, to) {
  var rest = this.slice((to || from) + 1 || this.length);
  this.length = from < 0 ? this.length + from : from;
  return this.push.apply(this, rest);
}

// function, takes and gives array, removes all emty elements and flatens content
function putWords(arr) {
  for(var i = 0; i < arr.length; i++) {
    if(arr[i] == "")
      arr.remove(i--);
    else
      arr[i] = arr[i].toLowerCase();
  }
  return arr;
}

// function, takes string and gives array of consisted words
const wordsArr = (s) => {
  return putWords(
    s.replace(new replaceWithSpaces(r1)).replace(new replaceWithSpaces(r2)).split(new makeMap(' '))
  );
}


// ––– OUTPUT –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– //

let arr = wordsArr(str); // arr = ["8foo", "bar8", "foo8bar", "foo", "bar", "foo_bar"]


// ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– //