Exclude property from type

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For versions of TypeScript at or above 3.5

In TypeScript 3.5, the Omit type was added to the standard library. See examples below for how to use it.

For versions of TypeScript below 3.5

In TypeScript 2.8, the Exclude type was added to the standard library, which allows an omission type to be written simply as:

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>

For versions of TypeScript below 2.8

You cannot use the Exclude type in versions below 2.8, but you can create a replacement for it in order to use the same sort of definition as above. However, this replacement will only work for string types, so it is not as powerful as Exclude.

// Functionally the same as Exclude, but for strings only.
type Diff<T extends string, U extends string> = ({[P in T]: P } & {[P in U]: never } & { [x: string]: never })[T]
type Omit<T, K extends keyof T> = Pick<T, Diff<keyof T, K>>

And an example of that type in use:

interface Test {
    a: string;
    b: number;
    c: boolean;
}

// Omit a single property:
type OmitA = Omit<Test, "a">; // Equivalent to: {b: number, c: boolean}

// Or, to omit multiple properties:
type OmitAB = Omit<Test, "a"|"b">; // Equivalent to: {c: boolean}

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