Watch Mouse: Find overlap between two strings + Java Script

Find overlap between two strings + Java Script

function findOverlap(a, b) {
  if (b.length === 0) {
    return "";
  }
 
  if (a.endsWith(b)) {
    return b;
  }
 
  if (a.indexOf(b) >= 0) {
    return b;
  }
 
  return findOverlap(a, b.substring(0, b.length - 1));
}

Some test cases:

findOverlap("12345", "aaa")
""
findOverlap("12345", "12")
"12"
findOverlap("12345", "345")
"345"
findOverlap("12345", "3456")
"345"
findOverlap("12345", "111")
"1"