30-seconds-of-code/snippets/is.md

title, tags, expertise, cover, firstSeen, lastUpdated

title	tags	expertise	cover	firstSeen	lastUpdated
Check if value is of type	type,array	intermediate	blog_images/coffee-phone-tray.jpg	2018-01-17T21:23:46+02:00	2020-10-20T23:02:01+03:00

Checks if the provided value is of the specified type.

• Ensure the value is not undefined or null using Array.prototype.includes().
• Use Object.prototype.constructor to compare the constructor property on the value with type to check if the provided value is of the specified type.

const is = (type, val) => ![, null].includes(val) && val.constructor === type;

is(Array, [1]); // true
is(ArrayBuffer, new ArrayBuffer()); // true
is(Map, new Map()); // true
is(RegExp, /./g); // true
is(Set, new Set()); // true
is(WeakMap, new WeakMap()); // true
is(WeakSet, new WeakSet()); // true
is(String, ''); // true
is(String, new String('')); // true
is(Number, 1); // true
is(Number, new Number(1)); // true
is(Boolean, true); // true
is(Boolean, new Boolean(true)); // true