JavaScript object vs. array lookup performance

Question

What is the performance difference between retrieving the value by key in a JavaScript object vs iterating over an array of individual JavaScript objects?

In my case, I

Answer 1

This problem touches all programming languages. It depends on many factors:

• size of your collection -arrays will get slower when you are searching for the last key, and array is quite long
• can elements repeat them selves-if yes, than you need a array. If no: you need either a dictionary (map) or you need to write a add method that for each add will iterate your array and find possible duplicates-that can be troublesome, when dealing with large lists
• average key usage - you will lose performance, if the most requested userId is at the end of the list.

In your example map would be a better solution. Secondly, you need to add a break to yor code:)

var user;

for (var i = 0; i < users.length; i ++) {
  if (users[i].id == id) {
     user = users[i]; break;
  }
}

Or you will lose performance:)