Sentence split https://jsfiddle.net/6msy9wpc/

sentence.js

// Given an input of a dictionary of words and an input senetnce that does not contain spaces, write a method that returns the input sentence split into words.

// Input: "applesauceisfun", ["apple","applesauce","is","good"]
// Output: "applesauce is fun"

const dict = ["apple","applesauce","is","good"];

// Simple approach with indexOf (uses shorter words).
const sentenceSplit = (s, dict) => {
	dict.sort((a, b) => { return b.length - a.length }).forEach(word => {
  	const start = s.indexOf(word);
    if (start !== -1) {
			const end = start + word.length;
      s = s.replace(word, ` ${word} `);
    }
  });
  
  return s.trim().replace(/  /g, ' ');
};

// Sliding window approach, finds longest fitting dictionary word.
const sentenceSplit2 = (s, dict) => {
  let left = 0;
	let right = s.length - 1;
  
  while (left < s.length && right > left) {
  	const word = s.substring(left, right + 1);
		if (dict.indexOf(word) !== -1) {
    	s = s.replace(word, ` ${word} `);
      
      left += word.length + 1 + 1;
      right = s.length;
    }
    else {
    	right--;
    }
  }
  
  return s.replace(/  /g, ' ').trim();
};

console.log(sentenceSplit('applesauceisgood', dict));
console.log(sentenceSplit2('applesauceisgood', dict));