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Sort array of objects by string property value in JavaScript

Sort array of objects by string property value in JavaScript

David Y.

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The ProblemJump To Solution

Given an array of similar JavaScript objects, how can I sort them by the value of a string property? For example, I would like to sort this array by the lastname property:

Click to Copy
const people = [
  { firstname: "John", lastname: "Smith" },
  { firstname: "Jane", lastname: "Doe" },
  { firstname: "Zinedine", lastname: "Zidane" },
  { firstname: "Aaron", lastname: "Aaronovitch" },
];

The Solution

JavaScript’s Array.sort method takes an optional comparison function, which we can define however we like. This function takes two elements, a and b, and should return a negative number if a < b, a positive number if a > b, and zero if they are equal.

We can use this to sort our array as follows:

Click to Copy
const people = [
  { firstname: "John", lastname: "Smith" },
  { firstname: "Jane", lastname: "Doe" },
  { firstname: "Zinedine", lastname: "Zidane" },
  { firstname: "Aaron", lastname: "Aaronovitch" },
];

function compare(a, b) {
  const aln = a.lastname.toLowerCase();
  const bln = b.lastname.toLowerCase();

  if (aln < bln) {
    return -1;
  }

  if (aln > bln) {
    return 1;
  }

  return 0;
}

people.sort(compare)

console.log(people)
// will print:
// [
//     { firstname: "Aaron", lastname: "Aaronovitch" },
//     { firstname: "Jane", lastname: "Doe" },
//     { firstname: "John", lastname: "Smith" },
//     { firstname: "Zinedine", lastname: "Zidane" },
// ]

Our comparison works by comparing the first letter of both strings passed to it, according to their position in the character set, for example A < Z. We convert both of the lastname strings to lowercase before comparing them. This is because string comparisons work with the position of characters in character sets, and so lowercase letters will always be sorted after uppercase letters. While this wouldn’t have presented a problem for this data set, it’s worth keeping in mind when sorting strings.

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