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‎README.md‎

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# Improved JavaScript Type Testing
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A robust alternative to JavaScript's `typeof` keyword.
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This is a JavaScript module that exports: [`is`](#is) (default)
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---
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A robust alternative to JavaScript's built-in type testing.
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## Get the type
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---
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### is()
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The **is()** function determines the type of its argument and returns a [Type](#the-type-class) object.
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## Type Names
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This module uses an expanded set of type names that make no distinction between primitive values and objects.
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For example, `5` and `new String(5)` are both of type "number".
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| Type Name | Values
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| - | -
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| array | `Array` objects
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| bigint | _bigint_ primitives
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| boolean | `false`, `true`, `Boolean` objects
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| date | `Date` objects
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| error | `Error` objects
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| function | `Function` objects
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| map | `Map` objects
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| nan | `NaN`
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| null | `null`
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| number | _number_ primitives, `Number` objects; excludes `NaN`
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| object | instances of `Object` that don't match another type in this list
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| promise | `Promise` objects
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| regex | `RegExp` objects
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| set | `Set` objects
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| string | _string_ primitives, `String` objects
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| symbol | _symbol_ primitives
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| undefined | `undefined`
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| weakmap | `WeakMap` objects
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| weakset | `WeakSet` objects
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## Determine a Type
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The **is()** function returns an object describing the type of its argument.
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Syntax:
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> `is(value)`
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Parameters:
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- ***value*** - The value to determine the type of.
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Return value:
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- A [Type](#the-type-class) object.
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### The Type class
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A String object storing a primitive type, with the following additional properties.
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> **is**(_value_)
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| Property | Type | Description
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| - | - | -
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| .**type** | string | The type name returned by the `typeof` operator.
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| .**objectType** | string | The object name used by `Object.prototype.toString()`. Undefined for primitive types.
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| .**primitive** | string | True for primitive types.
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| .**object** | string | True for object types.
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Returned object:
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| Property | Description
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| - | -
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| .**type** | The type name used by this module.
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| .**typeof** | The value returned by the `typeof` operator.
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| .**toStringTag** | The name used by `Object.prototype.toString()`.
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| .**constructorName** | The name of the argument's constructor, or `undefined`.
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| .**isObject** | True if the value is an object.
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| .**isPrimitive** | True if the value is a primitive.
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### Example
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<details>
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<summary>Examples</summary>
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```
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is(2).type; // "number"
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is(2).toString() // "number"
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is(2) == "number"; //true
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is(2).primitive; // true
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is(2).object; // undefined
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is(2).objectType; // undefined
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let o = new Number(2);
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is(o).type; // "number"
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is(o).toString() // "number"
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is(o) == "number"; //true
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is(o).primitive; // undefined
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is(o).object; // true
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is(o).objectType; // "Number"
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let v;
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is(v).type // "undefined"
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is(v).typeof // "undefined"
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is(v).toStringTag // "Undefined"
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is(v).constructorName // undefined
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v = null;
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is(v).type // "null"
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is(v).typeof // "object"
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is(v).toStringTag // "Null"
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is(v).constructorName // undefined
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v = NaN;
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is(v).type // "nan"
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is(v).typeof // "number"
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is(v).toStringTag // "Number"
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is(v).constructorName // "Number"
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v = 42;
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is(v).type // "number"
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is(v).typeof // "number"
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is(v).toStringTag // "Number"
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is(v).constructorName // "Number"
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v = new Number(42);
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is(v).type // "number"
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is(v).typeof // "object"
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is(v).toStringTag // "Number"
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is(v).constructorName // "Number"
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v = [];
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is(v).type // "array"
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is(v).typeof // "object"
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is(v).toStringTag // "Array"
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is(v).constructorName // "Array"
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v = ()=>{};
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is(v).type // "function"
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is(v).typeof // "function"
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is(v).toStringTag // "Function"
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is(v).constructorName // "Function"
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class Foo {}
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v = new Foo();
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is(v).type // "object"
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is(v).typeof // "object"
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is(v).toStringTag // "Object"
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is(v).constructorName // "Foo"
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class Bar {
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get [Symbol.toStringTag](){ return "Foobar"; }
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}
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v = new Bar();
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is(v).type // "object"
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is(v).typeof // "object"
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is(v).toStringTag // "Foobar"
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is(v).constructorName // "Bar"
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```
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---
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## Test for a type
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For each of the type-testing methods, the only parameter is the item to be tested. The return value is a boolean.
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</details>
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**is.object()**
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**is.primitive()**
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**is.undefined()**
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**is.null()**
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## Type Testing
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**is.number()** - A real number.
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**is.infinite()** \*
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**is.nan()** \*
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Each of the type-testing methods return a boolean indicating if the argument is of that type.
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\* Note that JavaScript doesn't correctly treat all undefined forms as `NaN`. For example, `1/0` and `0**0` are undefined forms, but JavaScript treats them as `Infinity`.
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**is.bigint()**
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**is.boolean()**
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**is.string()**
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**is.symbol()**
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**is.function()**
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**is.array()**
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**is.date()**
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**is.error()**
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**is.regexp()**
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**is.map()**
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**is.set()**
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**is.weakmap()**
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**is.weakset()**
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**is.promise()**
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Syntax:
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> is._typeTester_(_value_)
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### Basics
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| Method | Tests for
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| - | -
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| is.**function**() | instance of `Function`
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| is.**object**() | instance of `Object`
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| is.**primitive**() | primitives
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| is.**null**() | `null`
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| is.**nullish**() | `undefined`, `null`
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| is.**undefined**() | `undefined`
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| is.**defined**() | not `undefined`
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### Booleans
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| Method | Tests for
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| - | -
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| is.**boolean**() | `false`, `true`, instance of `Boolean`
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| is.**falsy**() | `false`, `undefined`, `null`, `NaN`, `0`, `-0`, `0n`, `""`, [`document.all`](https://developer.mozilla.org/en-US/docs/Web/API/Document/all#conversion_to_boolean)
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| is.**truthy**() | not falsy
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### Numbers
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| Method | Tests for
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| - | -
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| is.**bigint**() | _bigint_ primitive
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| is.**date**() | instance of `Date`
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| is.**numberish**() | _number_ primitive, instance of `Number`
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_Numberish_ values can be more explicitly tested using the following methods:
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| Method | Tests for
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| - | -
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| is.**real**() | real numbers
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| is.**infinite**() | `Infinity`, `-Infinity`
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| is.**number**() | real numbers, `Infinity`, `-Infinity`
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| is.**nan**() | `NaN`
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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`.
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### Text
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| Method | Tests for
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| - | -
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| is.**regex**() | instance of `RegExp`
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| is.**string**() | _string_ primitive, instance of `String`
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### Collections
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| Method | Tests for
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| - | -
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| is.**array**() | instance of `Array`
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| is.**map**() | instance of `Map`
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| is.**set**() | instance of `Set`
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| is.**weakmap**() | instance of `WeakMap`
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| is.**weakset**() | instance of `WeakSet`
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### Other Common Types
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| Method | Tests for
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| - | -
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| is.**error**() | instance of `Error`
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| is.**promise**() | instance of `Promise`
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| is.**symbol**() | _symbol_ primitive
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## Additional Methods
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| Method | Description
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| - | -
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| is.**empty**(_value_) | Tests if an object's `.length` or `.size` property equals zero.
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| is.**of**(_value_, _class_) | Tests if _value_ is an instance of _class_. (Same as using the `instanceof` operator.)

‎isType.mjs‎

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