JavaScript(TypeScript)

array_of_keys_of_type.ts

type Member = {
  id: string;
  firstName: string;
  lastName: string;
  age: number;
  salary: number;
};

for (const field of ['firstName', 'lastName', 'age', 'salary'] as Array<
  keyof Member
>) {
  console.log(field);
}

encodeURIComponent.js

// an example URI encoding when using the Instagram API
var apiUrl = 'https://api.instagram.com/v1/tags/';
apiUrl +=
  encodeURIComponent('何かしらのタグ名') +
  '/media/recent?client_id=' +
  clientId;

export_default_with_barrel.ts

export { default as MyModule } from 'src/MyModule';

property_names_from_class.ts

export type NonFunctionPropertyNames<T> = {
  [K in keyof T]: T[K] extends Function ? never : K;
}[keyof T];

export class Member {
  static PUBLIC_FIELDS: NonFunctionPropertyNames<Member>[] = [
    'id',
    'avatar',
    'firstName',
    'lastName',
    'department',
    'joinedAt',
    'phoneNumber',
    'email',
    'pr',
  ];
  static PRIVATE_FIELDS: NonFunctionPropertyNames<Member>[] = ['age', 'salary'];

  constructor(
    public id: string,
    public avatar: string,
    public firstName: string,
    public lastName: string,
    public age: number,
    public salary: number,
    public department: Department,
    public joinedAt: Date,
    public phoneNumber: string,
    public email: string,
    public pr: string
  ) {}
}

type_from_const.ts

// https://stackoverflow.com/a/53662389

export class AppError extends Error {
  code: ErrorCode;
  constructor(message: string, code: ErrorCode) {
    super(message);
    this.code = code;
  }
}

export const ErrorCodes = {
  USER_NOT_FOUND: 'user_not_found',
} as const;

type ErrorKey = keyof typeof ErrorCodes;
export type ErrorCode = typeof ErrorCodes[ErrorKey];