Find 'aeiou' in sentence

find_str_in_sent.js

function smallestSubStr(sentence, str) {
  if(!sentence || !str) { return null; }
  
  let searchStrIndex = 0;  
  let startsAtIndex;
  let smallestSubStrMap = {
    len: Number.MAX_SAFE_INTEGER,
    text: null
  };

  for(let index = 0; index < sentence.length; index++ ) {
    let isCharacterMatching = sentence[index].toLowerCase() === str[searchStrIndex].toLowerCase();
    let isStartCharacter = isCharacterMatching && startsAtIndex == undefined;
    let isEndCharacter = isCharacterMatching && searchStrIndex == str.length -1;

    if (isStartCharacter) {
      startsAtIndex = index;
    }
    
    if (isCharacterMatching) {
      searchStrIndex = searchStrIndex + 1;
    }
    
    if (isEndCharacter) {
      let strWidth = index - startsAtIndex;
      let isSmallestLengthSubStr = smallestSubStrMap.len > strWidth;
      
      if (isSmallestLengthSubStr) {
        let endIndex = index + 1;
        smallestSubStrMap.len = strWidth;
        smallestSubStrMap.text = sentence.substring(startsAtIndex, endIndex);
        startsAtIndex = undefined;
      }
      
      searchStrIndex = 0;
    }
  }
  
  if (smallestSubStrMap.len === Number.MAX_SAFE_INTEGER) {
    return null;
  }
  
  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)));