Typing

Since we are using typescript and there are many language features there are a number of standards to set in how things should be typed.

It is worth noting the verbage on some of these standards. Never/always should be followed however the usage of "preferred" or "rarely" means decisions are up to the programmer and should take some consideration. If a bad-practice of typing is required than it should be denoted in a PR description.

1. Assertions

Rarely use ‘as’ assertation, it just silences the compiler instead use an if statement to do type assertation.

script.typescript

if (!(x instance of Foo)) throw new Error("bad type");

2. Typing records

Always use ‘:’ as opposed to ‘as’ for records, this is because typescript compiler does not enforce type checking over records with ‘as’.

script.typescript

const foo = {  bar: 123,  bam: "abc",} as Foo; // bad!const foo: Foo = {  bar: 123,  bam: "abc",}; // good! Will throw error if wrong

Always use interfaces over the type alias for consistency. They are the same however we must pick one :)

script.typescript

interface User { // good!  firstName: string;  lastName: string;}type User = { // bad!  firstName: string,  lastName: string,}

3. General typing practice

Never use ‘any’ unless there is a specific reason which should always be documented with a comment and in the git PR, consider using unknown if appropriate.

Never use wrapper types. (i.e. String, Boolean, Number)

Always use strict equality === & !== to avoid unexpected bugs, unless there is supposed to be type flexibility (which shouldn't happen very often or at all).