fastest way to detect if a value is in a group of values in Javascript

Question

I have a group of strings in Javascript and I need to write a function that detects if another specific string belongs to this group or not.

What is the fastest way to achieve this? Is it alright to put the group of values into an array, and then write a function that searches through the array?

I think if I keep the values sorted and do a binary search, it should work fast enough. Or is there some other smart way of doing this, which can work faster?

Answer 1

Use a hash table, and do this:

// Initialise the set

mySet = {};

// Add to the set

mySet["some string value"] = true;

...

// Test if a value is in the set:

if (testValue in mySet) {
     alert(testValue + " is in the set");
} else {
     alert(testValue + " is not in the set");
}

Answer 2

You can use an object like so:

// prepare a mock-up object
setOfValues = {};
for (var i = 0; i < 100; i++)
  setOfValues["example value " + i] = true;

// check for existence
if (setOfValues["example value 99"]);   // true
if (setOfValues["example value 101"]);  // undefined, essentially: false

This takes advantage of the fact that objects are implemented as associative arrays. How fast that is depends on your data and the JavaScript engine implementation, but you can do some performance testing easily to compare against other variants of doing it.

If a value can occur more than once in your set and the "how often" is important to you, you can also use an incrementing number in place of the boolean I used for my example.