Maybe
Deno module inspired by Rusts Option<T>
to help handling null
and undefined
in Typescript.
How to use
The main idea is to type all values that are either T | null
or T | undefined
into a unified Maybe<T>
and to handle either cases with the help of match()
and the Matcher
class.
This allows solid type/null safety in your project without the fear of cannot read property name of undefined
.
Code example
import { Matcher, Maybe, match } from "https://deno.land/x/maybe/mod.ts";
import {
assert,
} from "https://deno.land/std@0.53.0/testing/asserts.ts";
async function saveFetch(url: string): Promise<Matcher<string>> {
const response: Maybe<string> = await fetch(url).then(
(res) => res.text(),
// Catch any error and map it to a nil value
).catch(() => null);
// Return a matcher
return match(response);
}
const ok: Matcher<string> = await saveFetch("https://example.com");
// We got a value
assert(ok.isOk());
// We can map the value to our liking
ok.map((s) => s.length).ok((val) => {
console.log("Page size:", val);
assert(val > 0);
});
// Errors do not crash our program but can be handled properly
const notOk: Matcher<string> = await saveFetch("https://example.cpm");
assert(notOk.isNil());
// It is save to work with the values even if we do not know if
// they are nil
notOk.map((s) => s.length).ok((val) => {
console.log("I will not be evaluated");
assert(false);
}).nil(() => {
// Runs if value does not exist
console.log("Value is nil");
assert(true);
});