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Typescript - Tips & Tricks - Advanced Types

puppo profile image Luca Del Puppo ・3 min read

Hi Guys,
Today I'll show you some advanced utilities exposed by the typescript language.
Let's start!

Utilities for Types

This utility allows you to add the optional modifier to all the properties of your type.

type PartialPoint = Partial<{ x: number; y: number }>; // { x?: number | undefined; y?: number | undefined; }
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This utility allows you to remove the optional modifier to all the properties of your type.

type RequiredPoint = Required<{ x?: number; y?: number }>; // { x: number; y: number; }
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This utility allows you to add the read-only modifier to all the properties of your type.

type ReadOnlyPoint = ReadOnly<{ x: number; y: number }>; // { readonly x: number; readonly y: number; }
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This utility allows you to get a subset of properties from another type.

type PickPoint = Pick<{ x: number; y: number }, "x">; // { x: number; }
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This utility allows you to exclude some properties from another type.

type OmitPoint = Omit<{ x: number; y: number }, "x">; // { y: number; }
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This utility allows you to map the properties of a type to another type.

type Point = {
  x: number;
  y: number;
};
type PointRecord = Record<keyof Point, number | null>; // { x: number | null; y: number | null; }
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This utility allows you to remove some types from a union type.

type ExcludeType = Exclude<"x" | "y", "x">; // "y"
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This utility allows you to get some types from a union type.

type ExtractType = Extract<"x" | "y", "x">; // "x"
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This utility allows you to remove the undefined and null types from a union type.

type NonNullableType = NonNullable<string | number | undefined | null>; // string | number
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Utilities for Function and Class

This utility allows you to extract from a function its parameters.

function createPoint(x: number, y: number) {
  return { x, y };
}
type ParametersType = Parameters<typeof createPoint>; // [x: number, y: number]
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This utility allows you to extract from a class its constructor parameters.

class Point {
  constructor(x: number, y: number) {}
}
type ConstructorParametersType = ConstructorParameters<typeof Point>; // [x: number, y: number]
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This utility allows you to get the return type from a function.

function createPoint(x: number, y: number) {
  return { x, y };
}
type CreatePointReturnType = ReturnType<typeof createPoint>; // { x: number; y: number; }
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This utility allows you to construct a type consisting of the instance type of a construction function type.

class Point {
  constructor(x: number, y: number) {}
}
type InstanceTypePoint = InstanceType<typeof Point>; // Point
type InstanceTypeString = InstanceType<string>; // Error: Type 'string' does not satisfy the constraint 'new (...args: any) => any'
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This utility allows you to extract the this parameter from a function type, or unknown if the function type has no this parameter.

function toHex(this: Number) {
  return this.toString(16);
}
function numberToString(n: ThisParameterType<typeof toHex>) {
  return toHex.apply(n);
}
numberToString(12)
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This utility allows you to remove the this parameter from a function type.

function toHex(this: Number) {
  return this.toString(16);
}
const fiveToHex: OmitThisParameter<typeof toHex> = toHex.bind(5);
fiveToHex()
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Utilities to Manipulation String Types

  • Uppercase

This utility allows converting your types to uppercase format.

type StringUppercase = Uppercase<"getX" | "getY" | "setX" | "setY">; // "GETX" | "GETY" | "SETX" | "SETY"
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  • Lowercase

This utility allows you to convert your types to lowercase format.

type StringLowercase = Lowercase<"getX" | "getY" | "setX" | "setY">; // "getx" | "gety" | "setx" | "sety"
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  • Capitalize

This utility allows you to convert your types to capitalize format.

type StringCapitalize = Capitalize<"getX" | "getY" | "setX" | "setY">; // "GetX" | "GetY" | "SetX" | "SetY"
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  • Uncapitalize

This utility allows you to convert your types to uncapitalize format.

type StringUncapitalize = Uncapitalize<"GetX" | "GetY" | "SetX" | "SetY">; // "getX" | "getY" | "setX" | "setY"
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I hope these utilities will help you in the future.
That's all for today.
See you soon Guys!

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