fastest way to determine if an element is in a sorted array

Question

I have an array of sorted ints with a 1,000 or more values (could be up to 5000+). I need to write a function that receives an int and returns a bool based on the element be

Answer 1

If doing lookups more than once, migrate to a map-like object.

var fastLookup = {};
mySortedArray.forEach(function(i){fastLookup[i]=true)});

//Each time:
  if (fastLookup[key]===true){ //do thing
  }