TIL how to check if the value is an array

POSTED ON: Jul 27, 2021

TAGS: javascript

Arrays aren't primatives or data structures.
so typeof doesn't work.

const arr = [1, 2, 3];

console.log(typeof arr); // object

console.log(Array.isArray(arr)); // true

From the MDN:

// all following calls return true
Array.isArray([]);
Array.isArray([1]);
Array.isArray(new Array());
Array.isArray(new Array('a', 'b', 'c', 'd'));
Array.isArray(new Array(3));
// Little known fact: Array.prototype itself is an array:
Array.isArray(Array.prototype);

// all following calls return false
Array.isArray();
Array.isArray({});
Array.isArray(null);
Array.isArray(undefined);
Array.isArray(17);
Array.isArray('Array');
Array.isArray(true);
Array.isArray(false);
Array.isArray(new Uint8Array(32));
Array.isArray({ __proto__: Array.prototype });

Via 17 Pro JavaScript tricks you didn't know

MDN:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray

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