Download this dictionary file and upload it to your project.

Fetch the dictionary file, and save it in a dictionary variable

// make an empty dictionary variable
let dictionary = {}

// fetch the dictionary file
let request = new XMLHttpRequest()
request.addEventListener(`load`, makeDictionary)
request.open(`GET`, `dictionary.txt`)
request.send()

// this function gets called after fetching the dictionary file
function makeDictionary() {
  // get all of the words in the file and save it to an array
  let words = this.response.split(/\r?\n/)

  // loop through the array of words
  for (let word of words) {
    // save each word in the dictionary variable
    dictionary[word] = true
  }
}

Use the dictionary variable where you want to determine if a word is an actual word

if (dictionary[word]) {
  // word is an actual word
}