Add PickFromPossiblyUndefined type

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 yarn.lock
+.idea

index.d.ts

@@ -39,6 +39,7 @@ export type {ConditionalExcept} from './source/conditional-except';
 export type {ConditionalKeys} from './source/conditional-keys';
 export type {ConditionalPick} from './source/conditional-pick';
 export type {ConditionalPickDeep, ConditionalPickDeepOptions} from './source/conditional-pick-deep';
+export type {PickFromPossiblyUndefined} from './source/pick-from-possibly-undefined';
 export type {UnionToIntersection} from './source/union-to-intersection';
 export type {Stringified} from './source/stringified';
 export type {FixedLengthArray} from './source/fixed-length-array';

readme.md

@@ -144,6 +144,7 @@ Click the type names for complete docs.
 - [`ConditionalKeys`](source/conditional-keys.d.ts) - Extract keys from a shape where values extend the given `Condition` type.
 - [`ConditionalPick`](source/conditional-pick.d.ts) - Like `Pick` except it selects properties from a shape where the values extend the given `Condition` type.
 - [`ConditionalPickDeep`](source/conditional-pick-deep.d.ts) - Like `ConditionalPick` except that it selects the properties deeply.
+- [`PickFromPossiblyUndefined`](source/pick-from-possibly-undefined.d.ts) - `Pick` properties from type that may be undefined.
 - [`ConditionalExcept`](source/conditional-except.d.ts) - Like `Omit` except it removes properties from a shape where the values extend the given `Condition` type.
 - [`UnionToIntersection`](source/union-to-intersection.d.ts) - Convert a union type to an intersection type.
 - [`LiteralToPrimitive`](source/literal-to-primitive.d.ts) - Convert a [literal type](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#literal-types) to the [primitive type](source/primitive.d.ts) it belongs to.

source/pick-from-possibly-undefined.d.ts

@@ -0,0 +1,32 @@
+/**
+`Pick` properties from type that may be undefined.
+
+@example:
+```
+import { PickFromPossiblyUndefined } from 'type-fest';
+
+type BillingDetails = {
+ taxId: string;
+ companyName: string;
+ address: string;
+ bankAccount: string;
+ ibanBankAccount: string;
+} | undefined;
+
+type CompanyBankAccounts = PickFromPossiblyUndefined<BillingDetails, 'bankAccount' | 'ibanBankAccount'>;
+
+const bankAccounts: CompanyBankAccounts = {
+ bankAccount: '123456789',
+ ibanBankAccount: '123456789',
+};
+
+await proceedPayment(bankAccounts);
+```
+
+@category Object
+ **/
+export type PickFromPossiblyUndefined<Type, Props extends keyof NonNullable<Type>> = Type extends undefined
+ ? never
+ : NonNullable<Type> extends object
+ ? Pick<NonNullable<Type>, Props>
+ : never;

test-d/pick-from-possibly-undefined.ts

@@ -0,0 +1,53 @@
+import {expectAssignable, expectType} from 'tsd';
+import {expectTypeOf} from 'expect-type';
+import type {PickFromPossiblyUndefined} from '../index';
+
+type BillingDetails = {
+ taxId: string;
+ companyName: string;
+ address: string;
+ bankAccount: string;
+ ibanBankAccount: string;
+} | undefined;
+
+type CompanyBankAccounts = PickFromPossiblyUndefined<BillingDetails, 'bankAccount' | 'ibanBankAccount'>;
+
+const bankAccounts: CompanyBankAccounts = {
+ bankAccount: '123456789',
+ ibanBankAccount: '123456789',
+};
+
+expectAssignable<CompanyBankAccounts>(bankAccounts);
+expectType<string>(bankAccounts.bankAccount);
+expectType<string>(bankAccounts.ibanBankAccount);
+expectTypeOf(bankAccounts).toMatchTypeOf({
+ bankAccount: '123456789',
+ ibanBankAccount: '123456789',
+});
+
+// Test what happens if type to pick from won't be undefined
+
+type AdminAccount = {
+ id: number;
+ roleId: number;
+ firstName: string;
+ lastName: string;
+ permissions: string[];
+};
+
+type UserAccount = PickFromPossiblyUndefined<AdminAccount, 'id' | 'firstName' | 'lastName'>;
+
+const userAccount: UserAccount = {
+ id: 1234,
+ firstName: 'Foo',
+ lastName: 'Bar',
+};
+
+expectAssignable<UserAccount>(userAccount);
+expectType<string>(userAccount.firstName);
+expectType<string>(userAccount.lastName);
+expectTypeOf(userAccount).toMatchTypeOf({
+ id: 1234,
+ firstName: 'Foo',
+ lastName: 'Bar',
+});