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Adding content to 111-utility-types
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# Partial
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# Partial
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The Partial type in TypeScript allows you to make all properties of a type optional. This is useful when you need to create an object with only a subset of the properties of an existing type.
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Here's an example of using the Partial type in TypeScript:
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```
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interface User {
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name: string;
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age: number;
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email: string;
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}
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function createUser(user: Partial<User>): User {
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return {
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name: 'John Doe',
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age: 30,
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email: 'john.doe@example.com',
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...user
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};
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}
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const newUser = createUser({ name: 'Jane Doe' });
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console.log(newUser);
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// Output: { name: 'Jane Doe', age: 30, email: 'john.doe@example.com' }
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```
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Learn more from the following links:
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- [Partial<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#partialtype)
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# Pick
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# Pick
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Pick constructs a type by picking the set of properties Keys (string literal or union of string literals) from Type.
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```
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interface Todo {
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title: string;
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description: string;
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completed: boolean;
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}
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type TodoPreview = Pick<Todo, "title" | "completed">;
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const todo: TodoPreview = {
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title: "Clean room",
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completed: false,
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};
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todo;
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const todo: TodoPreview
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```
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Learn more from the following links:
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- [Pick<Type, Keys>](https://www.typescriptlang.org/docs/handbook/utility-types.html#picktype-keys)
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# Omit
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# Omit
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Omit constructs a type by picking all properties from Type and then removing Keys (string literal or union of string literals).
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```
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interface Todo {
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title: string;
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description: string;
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completed: boolean;
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createdAt: number;
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}
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type TodoPreview = Omit<Todo, "description">;
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const todo: TodoPreview = {
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title: "Clean room",
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completed: false,
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createdAt: 1615544252770,
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};
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todo;
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const todo: TodoPreview
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type TodoInfo = Omit<Todo, "completed" | "createdAt">;
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const todoInfo: TodoInfo = {
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title: "Pick up kids",
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description: "Kindergarten closes at 5pm",
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};
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todoInfo;
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const todoInfo: TodoInfo
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```
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Learn more from the following links:
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- [Omit<Type, Keys>](https://www.typescriptlang.org/docs/handbook/utility-types.html#omittype-keys)
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# Readonly
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# Readonly
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Readonly constructs a type with all properties of Type set to readonly, meaning the properties of the constructed type cannot be reassigned.
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```
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interface Todo {
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title: string;
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}
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const todo: Readonly<Todo> = {
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title: "Delete inactive users",
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};
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todo.title = "Hello";
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Cannot assign to 'title' because it is a read-only property.
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```
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Learn more from the following links:
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- [Readonly<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype)
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# Record
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# Record
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Record constructs an object type whose property keys are Keys and whose property values are Type. This utility can be used to map the properties of a type to another type.
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```
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interface CatInfo {
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age: number;
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breed: string;
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}
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type CatName = "miffy" | "boris" | "mordred";
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const cats: Record<CatName, CatInfo> = {
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miffy: { age: 10, breed: "Persian" },
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boris: { age: 5, breed: "Maine Coon" },
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mordred: { age: 16, breed: "British Shorthair" },
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};
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cats.boris;
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const cats: Record<CatName, CatInfo>
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```
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Learn more from the following links:
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- [Record<Keys, Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#recordkeys-type)
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# Exclude
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# Exclude
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Exclude constructs a type by excluding from UnionType all union members that are assignable to ExcludedMembers.
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```
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type T0 = Exclude<"a" | "b" | "c", "a">;
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type T0 = "b" | "c"
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type T1 = Exclude<"a" | "b" | "c", "a" | "b">;
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type T1 = "c"
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type T2 = Exclude<string | number | (() => void), Function>;
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type T2 = string | number
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```
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Learn more from the following links:
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- [Exclude<UnionType, ExcludedMembers>](https://www.typescriptlang.org/docs/handbook/utility-types.html#excludeuniontype-excludedmembers)
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# Extract
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# Extract
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Extract constructs a type by extracting from Type all union members that are assignable to Union.
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```
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type T0 = Extract<"a" | "b" | "c", "a" | "f">;
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type T0 = "a"
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type T1 = Extract<string | number | (() => void), Function>;
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type T1 = () => void
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```
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Learn more from the following links:
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- [Extract<Type, Union>](https://www.typescriptlang.org/docs/handbook/utility-types.html#extracttype-union)
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# Non nullable
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# Non Nullable
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Nun Nullable constructs a type by excluding null and undefined from Type.
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```
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type T0 = NonNullable<string | number | undefined>;
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type T0 = string | number
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type T1 = NonNullable<string[] | null | undefined>;
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type T1 = string[]
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```
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Learn more from the following links:
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- [NonNullable<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#nonnullabletype)
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# Parameters
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# Parameters
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Parameters constructs a tuple type from the types used in the parameters of a function type Type.
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```
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declare function f1(arg: { a: number; b: string }): void;
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type T0 = Parameters<() => string>;
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type T0 = []
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type T1 = Parameters<(s: string) => void>;
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type T1 = [s: string]
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type T2 = Parameters<<T>(arg: T) => T>;
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type T2 = [arg: unknown]
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type T3 = Parameters<typeof f1>;
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type T3 = [arg: {
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a: number;
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b: string;
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}]
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type T4 = Parameters<any>;
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type T4 = unknown[]
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type T5 = Parameters<never>;
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type T5 = never
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type T6 = Parameters<string>;
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Type 'string' does not satisfy the constraint '(...args: any) => any'.
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type T6 = never
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type T7 = Parameters<Function>;
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Type 'Function' does not satisfy the constraint '(...args: any) => any'.
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Type 'Function' provides no match for the signature '(...args: any): any'.
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type T7 = never
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```
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Learn more from the following links:
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- [Parameters<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#parameterstype)
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# Return type
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# Return type
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Return type constructs a type consisting of the return type of function Type.
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```
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declare function f1(): { a: number; b: string };
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type T0 = ReturnType<() => string>;
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type T0 = string
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type T1 = ReturnType<(s: string) => void>;
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type T1 = void
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type T2 = ReturnType<<T>() => T>;
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type T2 = unknown
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type T3 = ReturnType<<T extends U, U extends number[]>() => T>;
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type T3 = number[]
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type T4 = ReturnType<typeof f1>;
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type T4 = {
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a: number;
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b: string;
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}
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type T5 = ReturnType<any>;
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type T5 = any
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type T6 = ReturnType<never>;
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type T6 = never
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type T7 = ReturnType<string>;
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Type 'string' does not satisfy the constraint '(...args: any) => any'.
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type T7 = any
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type T8 = ReturnType<Function>;
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Type 'Function' does not satisfy the constraint '(...args: any) => any'.
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Type 'Function' provides no match for the signature '(...args: any): any'.
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type T8 = any
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```
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Learn more from the following links:
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- [ReturnType<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#returntypetype)
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# Instance type
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# Instance type
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This type constructs a type consisting of the instance type of a constructor function in Type.
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```
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class C {
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x = 0;
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y = 0;
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}
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type T0 = InstanceType<typeof C>;
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type T0 = C
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type T1 = InstanceType<any>;
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type T1 = any
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type T2 = InstanceType<never>;
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type T2 = never
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type T3 = InstanceType<string>;
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Type 'string' does not satisfy the constraint 'abstract new (...args: any) => any'.
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type T3 = any
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type T4 = InstanceType<Function>;
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Type 'Function' does not satisfy the constraint 'abstract new (...args: any) => any'.
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Type 'Function' provides no match for the signature 'new (...args: any): any'.
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type T4 = any
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```
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Learn more from the following links:
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- [InstanceType<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#instancetypetype)
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# Awaited
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# Awaited
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This type is meant to model operations like await in async functions, or the .then() method on Promises - specifically, the way that they recursively unwrap Promises.
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```
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type A = Awaited<Promise<string>>;
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type A = string
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type B = Awaited<Promise<Promise<number>>>;
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type B = number
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type C = Awaited<boolean | Promise<number>>;
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type C = number | boolean
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```
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Learn more from the following links:
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- [Awaited<Type>](https://www.typescriptlang.org/docs/handbook/utility-types.html#awaitedtype)
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# Utility types
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# Utility Types
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TypeScript provides several utility types that can be used to manipulate and transform existing types. Here are some of the most common ones:
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1. Partial: makes all properties of a type optional.
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2. Readonly: makes all properties of a type read-only.
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3. Pick: allows you to pick specific properties from a type.
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4. Omit: allows you to omit specific properties from a type.
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5. Exclude: creates a type that is the set difference of A and B.
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Learn more from the following links:
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- [TypeScript - Utility Types](https://www.typescriptlang.org/docs/handbook/utility-types.html)
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