Package Exports

ts-simple-type

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Readme

ts-simple-type

What is this?

Right now the type checker for Typescript API doesn't expose methods like isAssignableTo. See issue #9879 on the Typescript github repository which has been open for 2.5 years.

To fill in the gap while this issue is being discussed and resolved this library aims to provide the most essential helper functions for working with types in Typescript.

This library has more than 300 tests comparing results to actual Typescript diagnostics.

How to use

To make it easier to work with types this library converts them to the interface SimpleType. Most functions in this library work with both SimpleType and the known and loved Typescript-provided Type interface.

The API is very simple. For example if you want to see if "typeB" is assignable to "typeA", you can use the following function.

import { isAssignableToType } from "ts-simple-type";

const isAssignable = isAssignableToType(typeA, typeB, typeChecker);

API Documentation

Check assignability

`isAssignableToType(typeA: Type | SimpleType, typeB: Type | SimpleType, checker: TypeChecker): boolean`

Returns if typeB is assignable to typeA.

`isAssignableToPrimitiveType(type: Type | SimpleType, checker: TypeChecker): boolean;`

`isAssignableToSimpleTypeKind(type: Type | SimpleType, kind: SimpleTypeKind | SimpleTypeKind[], options: IAssignableToSimpleTypeKindOptions): boolean;`

isAssignableToType(typeA: Type | SimpleType, typeB: Type | SimpleType, checker: TypeChecker): boolean;

isAssignableToValue(type: SimpleType | Type, value: any, checker: TypeChecker): boolean;

simpleTypeToString(type: SimpleType): string;

toSimpleType(type: Type, options: IToSimpleTypeOptions): SimpleType;

SimpleType

The SimpleType interface can also be used to construct your own types for typechecking.

import { SimpleType, SimpleTypeKind } from "ts-simple-type";

const colors: SimpleType = {
    kind: SimpleTypeKind.UNION,
    types: [
        { kind: SimpleTypeKind.STRING_LITERAL, value: "RED" },
        { kind: SimpleTypeKind.STRING_LITERAL, value: "GREEN" },
        { kind: SimpleTypeKind.STRING_LITERAL, value: "BLUE" }
    ]
}

simpleTypeToString(colors)
> "RED" | "GREEN" | "BLUE"

isAssignableToType(colors, { kind: SimpleTypeKind.STRING_LITERAL, value: "YELLOW" })
> false

isAssignableToValue(colors, "BLUE")
> true

isAssignableToValue(colors, "PINK")
> false