Simple TypeScript user-defined type guards generator.

1. Annotate type guard with @assertype

interface Foo
{
  a: string;
  b: number;
  c: boolean;
}

/** @assertype */
function Foo() {}

2. Run npx assertype tsconfig.json

tsconfig.json is path to your tsconfig

interface Foo
{
  a: string;
  b: number;
  c: boolean;
}

/** @ts-ignore @assertype */ // eslint-disable-next-line
function Foo(v): v is Foo { return typeof v === "object" && v !== null && typeof v.a === "string" && typeof v.b === "number" && typeof v.c === "boolean"; }

3. Get your type guard 🥳

• Type guard name must be the same as type name.
• Type guard must be defined in the same file as type.

Generator supports both interface and type declarations.

About ${number} template literal

TypeScript's ${number} is kinda weird. It tries to follow JS's number coercion algorithm, i.e:

• +"10" => 10
• +" " => 0
• +"       " => 0
• +"\n" => 0
• +"\r\n" => 0
• +"10e1" => 100
• +"10e-1" => 1

But "" results in error, even though in JS

• +"" => 0

So for now generator does not support ${number} template literal. If you need to check for an actual integers, you can use ${bigint} which is consistent with TypeScript and produces /-?\d+/ for checking numbers, so only valid values are:

• 1
• -12
• etc.

If you need support for floating point numbers or TypeScript's strange ${number} bahaviour please open an issue.

About ${boolean} template literal

Never ever use ${boolean} as TypeScript, for some reason, parses it as "false", so your typechecking will not be valid.