Obed

Why Array.includes() Fails With Nested Arrays

#javascript#arrays

If you try to check if a nested array exists in an array of arrays, you’ll get an unexpected result:

const matrix = [[1,2], [2,3]];
console.log(matrix.includes([1,2])); // false

You’d expect true, but JavaScript returns false. Here’s why.

The Problem: Reference vs. Value

JavaScript compares arrays by reference (memory location), not by value (contents). Even though [1,2] looks identical, it’s a different object in memory:

[1,2] === [1,2] // false, different objects!

So includes() can’t find a match because it’s looking for the exact same object, not one with the same contents.

Solution: Using some()

Use some() with a comparison function to check array contents:

const matrix = [[1,2], [2,3]];
const target = [1,2];

const found = matrix.some(arr =>
  JSON.stringify(arr) === JSON.stringify(target)
);
console.log(found); // true

This converts both arrays to strings for comparison, effectively checking their contents.

Limitations of JSON.stringify

  • Order-sensitive: [1,2] and [2,1] are different.
  • Non-serializable values: functions, undefined, and Symbol are lost or omitted.
  • Circular references: will throw an error.
  • Type coercion: JSON.stringify([1, "1"]) vs other subtle differences.