A Common-Sense Guide to Data Structures and Algorithms in JavaScript, Volume 1

Hash Table Lookups

When we look up items from a hash table, we use a key to find its associated value. Let’s see how this works with our Quickasaurus example hash table.

Suppose we want to look up the value associated with the key "bad". In our code, we’d say this:

thesaurus["bad"]

To find the value associated with "bad", the computer executes two simple steps:

1. The computer hashes the key we’re looking up: BAD = 2 * 1 * 4 = 8.
2. Since the result is 8, the computer looks inside cell 8 and returns the value stored there. In this case, that is the string "evil".

Let’s take a step back and look at the big picture here. In a hash table, the placement of each value is determined by its key; that is, by hashing the key itself, we compute the index number ...