mtparet/typeguard

TypeScript predicates and assertions library

ts-predicate

Getting started

yarn add ts-predicate
# or
npm install ts-predicate

Documentation

• TypeAssertion
• TypeGuard
• TypeHint
• ValueGuard

TypeAssertion

IsDefined

static IsDefined(value: unknown): void

Asserts that the value is not nullable, nor NaN.

IsBoolean

static IsBoolean(value: unknown): void

Asserts that the value is a boolean.

IsNumber

static IsNumber(value: unknown): void

Asserts that the value is a number, but not NaN.

IsInteger

static IsInteger(value: unknown): void

Asserts that the value is a safe integer.

IsFiniteNumber

static IsFiniteNumber(value: unknown): void

Asserts that the value is a number, but not NaN nor +/-Infinity.

IsString

static IsString(value: unknown): void

Asserts that the value is a string.

IsArray

static IsArray(value: unknown, constraints?: ArrayConstraints): void

Asserts that the value is an array.

The optional parameter constraints accept an object described by the following interface.

interface ArrayConstraints<T>
{
	minLength?: number;
	itemGuard?: (item: unknown) => item is T;
}

If minLength is provided, it'll asserts that the value has at least that many items.
If itemGuard is provided, it'll asserts that the predicate hold true for every item.

IsPopulatedArray

static IsPopulatedArray(value: unknown, constraints?: ArrayConstraints): void

Like IsArray, but asserts that the array is never empty too.

IsRecord

static IsRecord(value: unknown): void

Asserts that the value is a record: an object with no prototype, or directly using Object prototype.

IsObject

static IsObject(value: unknown): void

Asserts that the value is an object.

IsFunction

static IsFunction(value: unknown): void

Asserts that the value is a function, generator function, method, or class.

IsCallable

static IsCallable(value: unknown): void

Asserts that the value is not constructible.

HasNullableProperty

static HasNullableProperty(value: object, property: string): void

Asserts that the value is an object with the property defined, though it may be nullish or NaN.

HasProperty

static HasProperty(value: object, property: string): void

Asserts that the value is an object with the property defined.

TypeGuard

IsPrimitive

static IsPrimitive(value: unknown): boolean

Narrow down the value to being nullish, NaN, a boolean, a number, or a string.

IsDefined

static IsDefined(value: unknown): boolean

Narrow down the value to being not nullable, nor NaN.

IsBoolean

static IsBoolean(value: unknown): boolean

Narrow down the value to being a boolean.

IsNumber

static IsNumber(value: unknown): boolean

Narrow down the value to being a number, but not NaN.

IsInteger

static IsInteger(value: unknown): boolean

Narrow down the value to being a safe integer.

IsFiniteNumber

static IsFiniteNumber(value: unknown): boolean

Narrow down the value to being a number, but not NaN nor +/-Infinity.

IsString

static IsString(value: unknown): boolean

Narrow down the value to being a string.

IsArray

static IsArray(value: unknown, constraints?: ArrayConstraints): boolean

Narrow down the value to being an array.

The optional parameter constraints accept an object described by the following interface.

interface ArrayConstraints<T>
{
	minLength?: number;
	itemGuard?: (item: unknown) => item is T;
}

If minLength is provided, it'll confirm that the value has at least that many items.
If itemGuard is provided, it'll confirm that the predicate hold true for every item.

IsPopulatedArray

static IsPopulatedArray(value: unknown, constraints?: ArrayConstraints): boolean

Like IsArray, but narrow it to being a populated array.

IsRecord

static IsRecord(value: unknown): boolean

Narrow down the value to being a record: an object with no prototype, or directly using Object prototype.

IsObject

static IsObject(value: unknown): boolean

Narrow down the value to being an object.

IsFunction

static IsFunction(value: unknown): boolean

Narrow down the value to being a function, generator function, method, or class.

IsCallable

static IsCallable(value: unknown): boolean

Narrow down the value to being not constructible.

HasNullableProperty

static HasNullableProperty(value: object, property: string): boolean

Narrow down the value to being an object with the property defined, though it may be nullish or NaN.

HasProperty

static HasProperty(value: object, property: string): boolean

Narrow down the value to being an object with the property defined.

TypeHint

GetBaseType

static GetBaseType(value: any): string

Return a string depending on the type of the given value.

Possible values:

• undefined
• null
• NaN
• boolean
• number
• string
• array
• object
• function
• generator
• class

Note: generator refers to a generator function.

GetDetailedType

static GetDetailedType(value: any): string

Return a string depending on the type of the given value.
Provide more details than GetBaseType.

Possible values:

• undefined
• null
• NaN
• boolean (true or false)
• number (N)
• string (N characters)
• array (N items)
• anonymous object
• object anonymous class
• object ClassName
• anonymous function
• function name
• anonymous generator
• generator name
• anonymous class
• class Name

Note: generator refers to a generator function.

GetName

static GetName(value: any): string|undefined

If given a function, generator function, method, or class, return its name.
If given an object, return its constructor name.
If the given value doesn't have a name, return an empty string.
For any other value, return undefined.

ValueGuard

IsSimilar

static IsSimilar(a: any, b: any): boolean

Return true in the following cases :

• The same value has been passed as both arguments.
• Similar primitive values have been passed as arguments.
• Deeply similar arrays or records have been passed as arguments.

Otherwise, return false.