assert-util-types

TypeScript verifies that your program uses the right type as you write code, avoiding potential issues at runtime. but, By using any, you expose yourself to issues that are difficult to trace and debug, especially once the code is deployed in production.

when we cannot determine the type because we don’t know the result of that library and fetched data. we need to use any type for them.

So, if you dont want to use any type. you can use assert-util-types.

⚙️ Installation

case: use npm

$ npm install assert-util-types

case: use yarn

$ yarn add assert-util-types

case: use pnpm

$ pnpm install assert-util-types

📝 Usage

Nominal

nominal types is preventing confusion between two types. In regular Typescript you run into this problem:

type User = {
    id: number
    name: string
}

type Admin = {
    id: number
    name: string
}

const mike: Admin = {
    id: 1,
    name: 'mike'
}
const introduceMe = (props: User):string => {
    const {id, name} = props;
    return `No.${id}, User is ${name} !`
}
// oh... compilation was successful.
introduceMe(mike); // we can use User and Admin in the same way.

but Nominal type solve this problem

import { Nominal } from 'assert-util-types';

type userId = Nominal<number, 'userId'>
type adminId = Nominal<number, 'adminId'>

type User = {
    id: userId
    name: string
}

type Admin = {
    id: adminId
    name: string
}

const mike = {
    id: 1,
    name: 'mike'
} as Admin


const introduceMe = (props: User):string => {
    const {id, name} = props;
    return `No.${id}, User is ${name} !`
}

// That's great! get an error! 
introduceMe(mike); // Argument of type 'Admin' is not assignable to parameter of type 'User'.

user defined type guard

asSomething functions to create the more complex type checks. this functions passed the value in a value field upon success, or provides detailed error messages upon failure.

isString

import { isString } from 'assert-util-types';

isString('hello');  // true
isString(1);    // false

assertString

import { assertString } from 'assert-util-types';

assertString('hello', 'target'); // ok
assertString(1, 'target'); // throw error

asString

import { asString } from 'assert-util-types';

asString('hello', 'target'); // 'hello'
asString(1, 'target'); // error message is "target should be string"

isFilledString

import { isFilledString } from 'assert-util-types';

isFilledString('hello'); // true 
isFilledString(''); // false 
isFilledString(1); // false

assertFilledString

import { asFilledString } from 'assert-util-types';

asFilledString('hello', 'target'); // ok 
asFilledString('', 'empty string'); // error message is "empty string should have least 1 character" 
asFilledString(1, 'target'); // error message is "target should have least 1 character"

asFilledString

import { asFilledString } from 'assert-util-types';

asFilledString('hello', 'target'); // 'hello'

asFilledString('', 'empty string'); // error message is "empty string should have least 1 character" 
asFilledString(1, 'target'); // error message is "target should have least 1 character"

isNumber

import { isNumber } from 'assert-util-types';

isNumber(1); // true
isNumber(NaN) // false
isNumber('1'); // false

assertNumber

import { assertNumber } from 'assert-util-types';

assertNumber(1, 'target'); // ok
assertNumber(NaN, 'NaN'); // error message is "NaN should be number"

asNumber

import { asNumber } from 'assert-util-types';

asNumber(1, 'target'); // 1
asNumber(true, 'target'); // 1 
asNumber('hello', 'NaN'); // TypeError: Cannot convert hello to number

isFilledArray

import { isFilledArray } from 'assert-util-types';

isFilledArray(['string', 'number']); // true
isFilledArray([]); // false
isFilledArray(1); // false

assertFilledArray

import { assertFilledArray } from 'assert-util-types';

assertFilledArray(['string', 'number'], 'target'); // ok
assertFilledArray([], 'empty array'); // error message is "empty array should have least 1 item"

isObject

import { isObject } from 'assert-util-types';

isObject({}); // true
isObject([]); // false
isObject(1); // false

assertObject

import { assertObject } from 'assert-util-types';

assertObject({}); // ok
assertObject([], 'array'); // error message is "array should be object"

assertMatchedType

import { assertMatchedType } from 'assert-util-types';

type User = {
  id?: any;
  name?: string;
  email: string;
};

const obj: unknown = { id: 1, name: "foo" };

assertMatchedType<User>(obj, ["email"]); // throws error

Licence

MIT

knj-labo/assert-util-type