Javascript function that implements binary search algorithm

binary-search.js

function binarySearch( array, item ) {
  let low =  0;
  let high = array.length - 1;
  
  while ( low <= high ) {
    let mid = Math.floor( ( low + high ) / 2 );
    let guess = array[ mid ];
    
    if ( guess > item ) {
      high = mid - 1; 
    }
    else if ( guess < item ) {
      low = mid + 1;
    }
    else {
      return guess; 
    }
  }
  
  return null;
}