assign-uniform

Deterministic Uniform Assignment in Nodejs

Deterministically select an index for accessing an array. Primarily used for a/b testing.

Implementation adapted from Facebook's planout library.

Example

import assign from "assign-uniform";
 
const myArray = ["a", "b", "c"];
 
// a consistent identifier to be used for future assignment
const userId = "my-user-id";
 
// a unique salt for this array to assure independent assignments
const saltString = "myArray";
 
const i = assign(`${userId}.${saltString}`, myArray.length);
 
const deterministicAssignment = myArray[i];

Assuring independent assignments

If you are running uniform assignment across multiple arrays, for example running multiple a/b tests, and would like the arrays to be independent from each other (and probably you do); then it is important that each independent array has a unique salt that is part of the hash string.