TypeScript Methods Reference

Constructs a type with all properties of Type set to optional. Useful for update operations where you only need to specify changed fields.

Constructs a type with all properties of Type set to required. The opposite of Partial.

Constructs a type with all properties of Type set to readonly. Prevents reassignment of properties.

Constructs an object type whose property keys are Keys and whose property values are Type. Useful for mapping one type to another.

Constructs a type by picking the set of properties Keys from Type.

Constructs a type by picking all properties from Type and then removing Keys.

Constructs a type by excluding from UnionType all union members that are assignable to ExcludedMembers.

Constructs a type by extracting from Type all union members that are assignable to Union.

Constructs a type by excluding null and undefined from Type.

Constructs a type consisting of the return type of function Type.

Constructs a tuple type from the types used in the parameters of a function type.

Recursively unwraps the "awaited type" of a type. Useful for modeling await in async functions or Promise.all.

Constructs a type consisting of the instance type of a constructor function type.

Constructs a tuple type from the types of a constructor function parameter types.

Marks the contextual this type in an object literal. Useful for defining methods that have access to a specific this type.

Captures the type of a value or variable. Useful for inferring types from existing values.

Produces a union of the property names (keys) of an object type.

Defines a user-defined type guard. When the function returns true, TypeScript narrows the type.

Defines an assertion function that throws if condition is false. TypeScript narrows the type after the assertion.

Creates a readonly type with literal types instead of general types. Makes arrays become readonly tuples and objects deeply readonly.

Validates that an expression is assignable to a type without changing the inferred type. Preserves literal types while ensuring type safety.

Creates a new type by transforming properties of an existing type. Foundation for utility types like Partial and Readonly.

Creates a type that depends on a condition. If T extends U, the type is X, otherwise Y.

Declares a type variable within a conditional type that can be referenced in the true branch.

Creates string literal types by interpolating other types. Enables powerful string manipulation at the type level.

Converts each character in the string type to uppercase.

Converts each character in the string type to lowercase.

Converts the first character of the string type to uppercase.

Converts the first character of the string type to lowercase.

Represents an array of elements of type T. Both Array<T> and T[] syntaxes are equivalent.

Represents an immutable array. Prevents push, pop, and direct element assignment.

Fixed-length array where each element can have a different type. Position determines the type.

Describes objects that can have any number of properties with the specified key and value types.

Built-in type representing all possible property key types in JavaScript.

Allows a function to have multiple type signatures. TypeScript selects the appropriate signature based on arguments.

Functions that work with multiple types while maintaining type relationships. Type parameters are inferred from arguments.

Restricts generic type parameters to types that satisfy certain requirements.