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is

TS JS Deno

Checks if the provided value is of the specified type String name or Class itself.

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

typescript
type ConstructorType<T = any> = new (...args: any[]) => T;
export const is = (type: ConstructorType | string, val: any) =>
  ![, null].includes(val) &&
  (isString(type) ? val.constructor.name === type : val.constructor === type);
typescript
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

// With string name

is("Array", [1]); // true
is("ArrayBuffer", new ArrayBuffer(0)); // 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