compress.js

// https://www.codewars.com/kata/59de469cfc3c492da80000c5/train/javascript

function compress(sentence) {
  // Get all the words lower case in an array
  const words = sentence.split(" ").map(word => word.toLowerCase());
  // Get rid of all the duplicates
  const uniqueWords = words.filter( (word, index) => words.indexOf(word) === index );
  // Make a string of the position of each word in the non-duplicates array
  return words.map(word => uniqueWords.indexOf(word)).join("");
}

palindrome.js

// https://www.codewars.com/kata/57a1fd2ce298a731b20006a4/train/javascript

function isPalindrome(x) {
  return x.toLowerCase() === x.toLowerCase().split("").reverse().join("");
}

vending-machine.js

// https://www.codewars.com/kata/586e6d4cb98de09e3800014f/train/javascript

class VendingMachine {
  constructor(items, money) {
    this.items = items;
    this.money = money;
  }
  
  vend(selection, itemMoney) {
    itemMoney = parseFloat(itemMoney);
    
    const item = this.items.find(item => item.code.toLowerCase() === selection.toLowerCase());
    
    // invalid item
    if(!item) {
      return "Invalid selection! : Money in vending machine = " + this.money.toFixed(2);
    }
    
    // not enough money
    if(item.price > itemMoney) {
      return "Not enough money!";
    }
    
    // out of stock
    if(item.quantity === 0) {
      return item.name + ": Out of stock!";
    }
    
    // add the money to the machine
    this.money += itemMoney;
    // remove the item from the machine
    item.quantity--;
    
    let message = "Vending " + item.name;
    
    // handle change
    if(item.price < itemMoney) {
      const change = itemMoney - item.price;
      // remove the change from the machine
      this.money -= change;
      message += " with " + change.toFixed(2) + " change.";
    }
    
    return message;
  }
}