Find 'aeiou' in sentence

find_str_in_sent_2.js

function smallestSubStr(sentence, str) {
  if(!sentence || !str) { return null; }

  let beginCharacter = str[0].toLowerCase();
  let probableMatches = [];
  let smallestSubStrMap = {
    len: Number.MAX_SAFE_INTEGER,
    text: null
  };
 
  for(let index = 0; index < sentence.length; index++ ) {
    let character = sentence[index].toLowerCase();
    let isBeginCharacter = character === beginCharacter;
    
    if (isBeginCharacter) {
        let nextLookUpIndex = 1;
        let probableMatch = {
          startsAtIndex: index,
          nextLookUpIndex: nextLookUpIndex
        }
        
        probableMatches.push(probableMatch);
    } else {
        probableMatches = probableMatches.filter(probableMatch => {
          let lookUpIndex = probableMatch.nextLookUpIndex;
          let isCharacterMatching = character === str[lookUpIndex].toLowerCase();
          let isEndCharacter = isCharacterMatching && lookUpIndex === str.length-1;

          if (isEndCharacter) {
              let lengthOfSubStrFound = (index + 1) - probableMatch.startsAtIndex;
              let isSmallerLengthSubStr = smallestSubStrMap.len >= lengthOfSubStrFound;
              
              if (isSmallerLengthSubStr) {
                  let endIndex = index + 1;
                  smallestSubStrMap.len = lengthOfSubStrFound;
                  smallestSubStrMap.text = sentence.substring(probableMatch.startsAtIndex, endIndex)
              }
              return false;
          }
          
          if (isCharacterMatching) {
              probableMatch.nextLookUpIndex = probableMatch.nextLookUpIndex + 1;
          }
          return true;
        });
    }
  };
  
  return smallestSubStrMap.text;
}


let sentences = [ '', 'au', 'aeiou', 'Hello Aeio and U', 
                 'My name is santhosh and you are?', 'My name is santhosh and you are?! aeiou'];
let str = 'aeiou';
sentences.forEach(sentence => console.log(`\nsmallestSubStr('${sentence}', '${str}')`, '->', smallestSubStr(sentence, str)));