Pylon

Some useful functionalities.

Index

Type aliases

• ModifyProps
• PropsType
• TypeEqual
• UnionKeyOf
• UnionOmit
• UnionOptional

Type aliases

ModifyProps

Add, remove or replace properties of an object.

type T = { a: string; b: number };
type X1 = ModifyProps<T, 'a'>; // X1 = { b: number }
type X2 = ModifyProps<T, { c: string }>; // X2 = { a: string; b: number; c: string }
type X3 = ModifyProps<T, { a: boolean }>; // X3 = { a: boolean; b: number; }
type X4 = ModifyProps<T, 'a', { c: string }>; // X4 = { b: number; c: string }

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PropsType

Infer props type for React component X, i.e. functions, React.FC, React.PureComponent and React.Component, with or without defaultProps.

const Comp = (props: { a: string }) => <div />;
type Props = PropsType<typeof Comp>; // expect { a: string }

class Comp extends React.Component<{ a: string }> {
  render() {
    return <div />;
  }
}
type Props = PropsType<typeof Comp>; // expect { a: string, children?: ReactNode }

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TypeEqual

Test if types X and Y are identical.

https://github.com/piotrwitek/utility-types/blob/master/src/mapped-types.ts#L153-L157 https://stackoverflow.com/questions/52443276/how-to-exclude-getter-only-properties-from-type-in-typescript

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UnionKeyOf

Returns keys of a type (same as keyword keyof), or the union of keys of a union type.

This is to complement keyword keyof returning only intersection of keys for a union type.

type T = { a: string; b: number } | { b: boolean; c: number };
type X = keyof T; // X = 'b'
type Y = UnionKeyOf<T>; // Y = 'a' | 'b' | 'c'

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UnionOmit

Remove keys in K from type T. Works with union types as well.

The default Omit has an odd behavior for the follow code, while UnionOmit fixes it:

type T = { a: string; b: number } | { b: boolean; c: number };
type X = Omit<T, 'b'>; // X = {}
type Y = UnionOmit<T, 'b'>; // Y = { a: string } | { c: number }

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UnionOptional

Make keys from K optional in T. Works with union types as well.

type T = { a: string; b: number };
type X = UnionOptional<T, 'a'>; // X = { a?: string; b: number}

type T = { a: string; b: number } | { b: boolean; c: number };
type X = UnionOptional<T, 'a'>; // X = { a?: string; b: number} | { b: boolean; c: number }