A collection of total functions to replace TypeScript's built-in partial functions.
npm install total-functions
A collection of total functions to replace TypeScript's built-in partial functions.
Intended to be used with strictNullChecks enabled.
``shyarn
yarn add total-functions
The Functions
$3
The array index operator is not well-typed in TypeScript:
typescript
const a: object[] = [];
const b = a[0]; // b has type object, not object | undefined as you might expect
b.toString(); // boomconst record = { foo: "foo" } as Record;
const bar = record["bar"]; // bar has type string, not string | undefined
bar.toUpperCase(); // boom
` is a safe alternative:`typescript
import { get } from "total-functions";const b = get(a, 0); // b has type object | undefined
const bar = get(record, "bar"); // bar has type string | undefined
`Note that
will exclude undefined from the return type when there is enough type information to be confident that the result cannot be undefined. See the object and tuple examples below for examples where undefined is not included in the return type.More usage examples:
`typescript
// tuple
const xs = [1, 2, 3] as const;
const x1 = get(xs, 1); // 2
const x100 = get(xs, 100); // undefined
const xMinus1 = get(xs, -1); // undefined
xs.map(x => x / 1 | 2 | 3 /);// array
const ys = [1, 2, 3];
const y1 = get(ys, 1); // number | undefined
const y100 = get(ys, 100); // number | undefined
ys.map(y => y / number /);
// sparse array
const zs = [1, , 2, 3];
const z1 = get(zs, 1); // number | undefined
const z100 = get(zs, 100); // number | undefined
zs.map(z => z / number | undefined /);
// readonly array
const as = [1, 2, 3] as ReadonlyArray<1 | 2 | 3>;
const a1 = get(as, 1); // 1 | 2 | 3 | undefined
const a100 = get(as, 100); // 1 | 2 | 3 | undefined
// record
const record = { 1: "asdf" } as Record;
const record1 = get(record, 1); // string | undefined
const record100 = get(record, 100); // string | undefined
// object
const obj = { 1: "asdf" };
const obj1 = get(obj, 1); // string
const obj100 = get(obj, 100); // doesn't compile
// const object
const constObj = { 1: "asdf" } as const;
const constObj1 = get(constObj, 1); // "asdf"
const constObj100 = get(constObj, 100); // doesn't compile
``There's also a corresponding ESLint rule to ban the unsafe array index operator.
See https://github.com/danielnixon/eslint-plugin-total-functions