A robust alternative to JavaScript's built-in type testing.
See the test page for examples.
This module uses an expanded set of type names that make no distinction between primitive values and objects.
For example, 5 and new Number(5) are both of type "number".
| Type Name | Values |
|---|---|
| array | Array objects |
| bigint | bigint primitives |
| boolean | false, true, Boolean objects |
| date | Date objects |
| error | Error objects |
| function | Function objects |
| map | Map objects |
| nan | NaN, Number objects with value NaN |
| null | null |
| number | number primitives, Number objects; excludes NaN values |
| object | instances of Object that don't match another type in this list |
| promise | Promise objects |
| regex | RegExp objects |
| set | Set objects |
| string | string primitives, String objects |
| symbol | symbol primitives |
| undefined | undefined |
| weakmap | WeakMap objects |
| weakset | WeakSet objects |
The is() function returns an object describing the type of its argument.
Syntax:
is(value)
Returned object:
| Property | Description |
|---|---|
| .type | The type name used by this module. |
| .typeof | The value returned by the typeof operator. |
| .toStringTag | The name used by Object.prototype.toString(). undefined for primitives. |
| .constructorName | The name of the argument's constructor. undefined for primitives. |
| .isObject | True if the value is an object. |
| .isPrimitive | True if the value is a primitive. |
Each of the type-testing methods return a boolean indicating if the argument is of that type.
Syntax:
is.typeTester(value)
| Method | Tests for |
|---|---|
| is.function() | instance of Function |
| is.object() | instance of Object |
| is.primitive() | primitives |
| is.null() | null |
| is.nullish() | undefined, null |
| is.undefined() | undefined |
| is.defined() | not undefined |
| Method | Tests for |
|---|---|
| is.boolean() | false, true, instance of Boolean |
| is.falsy() | false, undefined, null, NaN, 0, -0, 0n, "", document.all |
| is.truthy() | not falsy |
| Method | Tests for |
|---|---|
| is.bigint() | bigint primitive |
| is.date() | instance of Date |
| is.numberish() | number primitive, instance of Number |
Numberish values can be more explicitly tested using the following methods:
| Method | Tests for |
|---|---|
| is.real() | real numbers |
| is.infinite() | Infinity, -Infinity |
| is.number() | real numbers, Infinity, -Infinity |
| is.nan() | NaN |
Note that JavaScript doesn't always treat mathematical expressions of undefined or indeterminate form as you might expect. For example, 1/0 is an undefined form, but JavaScript evaluates it as Infinity.
| Method | Tests for |
|---|---|
| is.regex() | instance of RegExp |
| is.string() | string primitive, instance of String |
| Method | Tests for |
|---|---|
| is.array() | instance of Array |
| is.map() | instance of Map |
| is.set() | instance of Set |
| is.weakmap() | instance of WeakMap |
| is.weakset() | instance of WeakSet |
| Method | Tests for |
|---|---|
| is.error() | instance of Error |
| is.promise() | instance of Promise |
| is.symbol() | symbol primitive |
| Method | Description |
|---|---|
| is.empty(value) | Tests if an object's .length or .size property equals zero. |
| is.of(value, class) | Tests if value is an instance of class. (Same as using the instanceof operator.) |