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A few methods to check if all values in the JavaScript array are the same

Published: · 2 minutes read

There are many solutions to the same problem in programming, and that’s one of my favourite things about it. Checking if all the items in an array are the same is an interesting exercise, so let’s look at a few options.

  • We want to return false for ['Ed', 'Edd', 'Eddy']
  • We want to return true for ['Edd', 'Edd', 'Edd']
const f = (array) => array.every((item) => item === array[0]);

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

const f = ([first, ...rest]) => rest.every((item) => item === first);

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

const f = (array) => !array.some((item) => item !== array[0]);

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

const f = (array) => new Set(array).size === 1;

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

const f = (array) => {
  for (let index = 1; index < array.length; index++) {
    if (array[index] !== array[0]) {
      return false;
    }
  }

  return true;
};

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

const f = (array) => {
  const arraySorted = array.sort();
  return arraySorted[0] === arraySorted[array.length - 1];
};

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

import { uniq } from "lodash";

const f = (array) => uniq(array).length === 1;

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

import { without } from "lodash";

const f = (array) => !without(array, array[0]).length;

f(["Ed", "Edd", "Eddy"]); // false
f(["Edd", "Edd", "Edd"]); // true

From all the methods listed above, every and new Set() is my way to go. Nothing wrong with the good old for loop! Personally, for simple things like that, I wouldn’t use external libraries like lodash, but you do you.

That’s it for today. Can you think of any more solutions to solve this little problem? I am super curious what is your preference. For now, stay tuned for the next post and keep coding 👩‍💻 🧑‍💻

Comments

  • D
    Dan Jordan
    , #a5e77fb9

    Sorry for this...

    export function f(arr: Array<number | string>): boolean {
  const first = arr[0];
  const test = Array.from({ length: arr.length }, () => first);

  return arr.toString() === test.toString();
}

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