# Implementing Binary Search in JavaScript

This morning I worked through the binary search tutorial in the Algorithms class on Khan Academy. The concepts were familiar from when I took MIT's Introduction to Computer Science and Programming on EdX, but this time I learned to implement the algorithm in JavaScript rather than Python.

I also learned a quick way to unit test a function in JavaScript by using Program.assertEqual():

Here's the code for the algorithm with a few tests. (Hit the link to get the code on GitHub.)

```
/* Returns either the index of the location in the array,
or -1 if the array did not contain the targetValue */
var doSearch = function(array, targetValue) {
var min = 0;
var max = array.length - 1;
var guess;
var numGuesses = 0;
while(max <= min) {
numGuesses ++;
guess = Math.floor((min + max) / 2);
if ( array[guess] === targetValue ) {
println(numGuesses);
return guess;
} else if ( array[guess] < targetValue ) {
min = guess + 1;
} else {
max = guess - 1;
}
}
println(numGuesses);
return -1;
};
var primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37,
41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];
var result = doSearch(primes, 73);
println("Found prime at index " + result);
// Quick tests to verify results
Program.assertEqual(doSearch(primes, 73), 20);
Program.assertEqual(doSearch(primes, 7), 3);
Program.assertEqual(doSearch(primes, 25), -1);
```