bsitruk

Constrained Identity Function


- Use Case: We want to create a Record with a limited set of Keys, and a defined type of Values.
	- We also don't want to Type the Set of Keys, but leverage TypeScript inference instead (DRY)
- If we create a new inline object literal, TypeScript will prevent any new key from being added, by won't enforce the type of the Values.
	- So Narrow Keys, Wide Value Type
- If we specify the type Record<string, number>, we'll be able to add any new Key after the object creation
	- So Wide Keys, Narrow Value Type
- By using a Types Identity Function, we can build an object with enforced Value Type, and Narrow set of Keys.

bsitruk

// Sort List of Objects By Two Keys
type SortKey<T> = {
  key: keyof T;
  order: 1 | -1;
};
export function sortByKeys<T>(list: T[], keys: SortKey<T> | [SortKey<T>, SortKey<T>]) {
  if (!Array.isArray(keys)) {
    const { key: sortKey, order } = keys;
    return list.sort((v1, v2) => (v1[sortKey] < v2[sortKey] ? order * 1 : -1 * order));
  }

bsitruk

const keys = ['k1', 'k2', 'k3']
const Keys = typeof keys[number]

type Object = {
  k1: number,
  k2: boolean
}

type KeyValue = {
  [k in Keys]: k extends keyof Object ? Object[k] : unknown

bsitruk

import * as cluster from 'cluster';
import * as os from 'os';
import { Logger } from '@nestjs/common';

export class Cluster {
  static register(workers: number, logger: Logger, callback: CallableFunction): void {
    const cpuCount = os.cpus().length;

    if (cluster.isMaster) {
      logger.log(`master process started on ${process.pid}`);

bsitruk

Cypress.Commands.add('interceptOnce', (method, path, alias, status) => {
  cy.intercept({
    method,
    path,
    times: 1,
  }).as(alias);

  if (status) {
    return cy.wrap(() =>
      cy

bsitruk

function getCurrentDateP(mongoConnection) {
  const query = { _id: 1 };
  const update = { $currentDate: { updated_at: true } };
  const queryOptions = { upsert: true, returnOriginal: false };
  
  return mongoConnection
      .collection('current_date')
      .findOneAndUpdate(query, update, queryOptions)
      .then(mongoResult => mongoResult.value.updated_at)
}

bsitruk

.catch((err: Error | AxiosError) {
  if (axios.isAxiosError(error))  {
    // Access to config, request, and response
  } else {
    // Just a stock error
  }
})

bsitruk

<form
  ref={formRef}
  onSubmit={(e: React.SyntheticEvent) => {
    e.preventDefault();
    const target = e.target as typeof e.target & {
      email: { value: string };
      password: { value: string };
    };
    const email = target.email.value; // typechecks!
    const password = target.password.value; // typechecks!

bsitruk

import { mode } from '@chakra-ui/theme-tools';
import { extendTheme } from '@chakra-ui/core';

const styles = {
  global: props => ({
    ":root": {
      "--app-title-color": "#718096",
      "--card-minw": "160px",
      "--blackwhite": mode("black", "white")(props),
      "--whiteblack": mode("white", "black")(props),

bsitruk

# Run a docker registry
# https://docs.docker.com/registry/deploying/
docker run -d -p 5000:5000 \
              --restart=always \
              --name registry\
              -v /mnt/registry:/var/lib/registry \
              -e REGISTRY_HTTP_ADDR=0.0.0.0:5000 \
              registry:2
              
# Add private registry as insecure