ts-morph

Types

Types are accessed by calling .getType() on nodes that are typed. For example:

const type = parameter.getType();

There are other ways for accessing a type. For example:

const returnType = functionDeclaration.getReturnType();

Checking type is assignable to another type

Note: Requires ts-morph 22+

To check if a type is assignable to another type, use the isAssignableTo method:

if (stringLitType.isAssignableTo(stringType)) {
  // ...
}

Compiler Type

The underlying compiler type can be accessed via:

const compilerType = type.compilerType;

Apparent type

Given the following variable declaration:

const myVar = 4;

The type is 4 and the apparent type is Number.

Retrieve the apparent type via the following:

const apparentType = type.getApparentType();

Text

Getting the type text can be achieved by calling .getText():

const text = type.getText();

Sometimes this may not be good enough. If not, try to provide the enclosing node:

const text = type.getText(parameter);

Format it by providing TypeFormatFlags:

const text = type.getText(parameter, TypeFormatFlags.NoTruncation | TypeFormatFlags.WriteArrayAsGenericType);

Look at the declaration file for more available options for TypeFormatFlags.

Constraint and Default

const constraintType = type.getConstraint();
const defaultType = type.getDefault();

Intersection types

const intersectionTypes = type.getIntersectionTypes();

Union types

const unionTypes = type.getUnionTypes();

Properties

Get the properties or property of a type:

const properties = type.getProperties();
const prop1 = type.getProperty("prop1");
const prop2 = type.getProperty(p => p.getName() === "prop2");

Or the apparent properties:

const apparentProperties = type.getApparentProperties();
const prop1 = type.getApparentProperty("prop1");
const prop2 = type.getApparentProperty(p => p.getName() === "prop2");

Base types

const baseTypes = type.getBaseTypes();

Base type of a literal type

const numberType = numberLiteralType.getBaseTypeOfLiteralType();

Call signatures

const callSignatures = type.getCallSignatures();

Construct signatures

Get the construct signatures (new signatures) of a type:

const constructSignatures = type.getConstructSignatures();

Index types

Get either the string index type (ex. for { [index: string]: Date; } it would be Date) or the number index type (ex. for { [index: number]: object; } it would be object):

const stringIndexType = type.getStringIndexType();
const numberIndexType = type.getNumberIndexType();

Tuple element types

const tupleElements = type.getTupleElements();

For example, for the type [string, number], the above would return an array containing the type for string and number.

Non-nullable type

Gets the non-nullable type from a nullable type:

const nonNullableType = type.getNonNullableType();

For example, string | undefined would return string.

Type flags

This has information about the type, such as TypeFlags.BooleanLike.

const flags = type.getFlags();

Generally a method that starts with "is" exists on the type and you can easily use that instead of checking the flags (same with Object flags below).

Object flags

This has information about object types, such as ObjectFlags.Mapped.

const objectFlags = type.getObjectFlags();

Symbol

Get the symbol of the type if it exists:

const typeSymbol = type.getSymbol();

Alias symbol

const aliasSymbol = type.getAliasSymbol();

Alias type arguments

const aliasTypeArgs = type.getAliasTypeArguments();

Telling type

Use any of the following methods:

type.isAnonymous();
type.isAny();
type.isArray();
type.isBoolean();
type.isBooleanLiteral();
type.isClass();
type.isClassOrInterface();
type.isEnum();
type.isEnumLiteral();
type.isInterface();
type.isIntersection();
type.isLiteral();
type.isNull();
type.isNumber();
type.isNumberLiteral();
type.isObject();
type.isString();
type.isStringLiteral();
type.isTemplateLiteral();
type.isTuple();
type.isUndefined();
type.isUnion();
type.isUnionOrIntersection();
type.isUnknown();

If you see something that doesn't exist here and should (there's a lot missing), then please log an issue or submit a pull request.

Removing a Type

Remove a type or a return type from a node:

propertyDeclaration.removeType();
functionDeclaration.removeReturnType();

TODO

Not implemented. Getting...

• Enum member types
• Destructuring pattern
• More...?