Issue
Environment
TypeScript's version is 3.2.1 and "tsconfig.json" is like below.
{
"compilerOptions": {
"target": "es5",
"module": "commonjs",
"strict": true,
"noUnusedLocals": true,
"noUnusedParameters": true,
"noImplicitReturns": true,
"noFallthroughCasesInSwitch": true,
"esModuleInterop": true
}
}
Question
I'm looking for Partially "Partial" type in TypeScript.
type Entity = {
a: string,
b: string,
c?: string,
};
type Ham = MyType<Entity, 'b'>;
/**
* expected to equal
* {
* a: string,
* b?: string, // changed to be optional
* c?: string,
* };
*/
P.S. Titian and t7yang
Thank you for your replies. I checked your types then both types pass compiler's check!
const abc = { a: 'a', b: 'b', c: 'c' };
const ab = { a: 'a', b: 'b' };
const ac = { a: 'a', c: 'c' };
const a = { a: 'a' };
// by t7yang
let test1Abc: OptionalKey<Entity, 'b'> = abc;
let test1Ab: OptionalKey<Entity, 'b'> = ab;
let test1Ac: OptionalKey<Entity, 'b'> = ac;
let test1A: OptionalKey<Entity, 'b'> = a;
// by Titian Cernicova-Dragomir
let test2Abc: PickPartial<Entity, 'b'> = abc;
let test2Ab: PickPartial<Entity, 'b'> = ab;
let test2Ac: PickPartial<Entity, 'b'> = ac;
let test2A: PickPartial<Entity, 'b'> = a;
Solution
You can use Pick
in conjunction with Partial
to pick only the properties you want to make optional, while preserving the rest using Exclude
to get the keys excluding the ones passed in to make optional :
type Entity = {
a: string,
b: string,
c?: string,
};
type PickPartial<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>> & Partial<Pick<T, K>>
type Ham = PickPartial<Entity, 'b'>; // a, b? , c?
Answered By - Titian Cernicova-Dragomir
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