1. How you should not write code

1. How you should not write code.md

How you should not write code

This is an article from mini-series of How you should not write code. If you know how to write code and want to write better code. Please follow someone like Robert Martin.

di_1.js

const Service = require("./Service");
class ClientWithoutInjection {
  constructor() {
    this.service = new Service();
  }
  greet() {
    return "Hello " + this.service.getName();
  }
}
class ClientWithInjection {
  constructor(service) {
    this.service = service;
  }
  greet() {
    console.log(this.service.getName);
    return "Hello " + this.service.getName();
  }
}
exports.ClientWithInjection = ClientWithInjection;
exports.ClientWithoutInjection = ClientWithoutInjection;

di_2.js

const {
  ClientWithInjection,
  ClientWithoutInjection
} = require('./Client')
const Service = require('./Service')
describe('DI', function () {
  describe('Client', function () {
    it('check it', function () {
      const cw = new ClientWithInjection(new Service())
      const co = new ClientWithoutInjection()
      expect(cw.greet()).toBe(co.greet())
    });
  });
});

di_3.js

jest.mock('./Service', () => (function () {
  this.getName = () => "something else"
}));
const {
  ClientWithoutInjection
} = require('./Client')
describe('DI', function () {
  describe('Client', function () {
    it('check it', function () {
      const co = new ClientWithoutInjection()
      expect(co.greet()).toBe("Hello something else")
    });
  });
});

di_4.js

// Service.js
class Service {
  getName() {
    return "This is service";
  }
}
module.exports = Service;

imp_1.js

// nest/nest/nest/nest/nest/nest/nest.js
const Service = require('../../../../../../dependency_injection/client/Service')console.log(new Service().getName())
// package.json
"scripts": {
  "nestWithout": "node nest/nest/nest/nest/nest/nest/nest.js",
  "test": "jest"
},

imp_2.js

// package.json
"scripts": {
    "nest": "NODE_PATH=./ node nest/nest/nest/nest/nest/nest/nest.js",
    "nestWithout": "node nest/nest/nest/nest/nest/nest/nest.js",
    "test": "jest"
  },
// nest/nest/nest/nest/nest/nest/nest.js
const Service2 = require('dependency_injection/client/Service')
console.log(new Service2().getName())

loop_1.js

// Program:: remove all odds and multiply 5, so that u get all numbers divisible by 10
//Data set
let data = [1, 2, 3, 4, 5];
const MULTIPLIER = 5;
//Data set
//Example 1
let mapped = [];
for (let index = 0, len = data.length; index < len; index++) {
  if (data[index] % 2 == 0) mapped.push(data[index] * MULTIPLIER);
}
console.log(mapped);

loop_2.js

//Example 2
mapped = data.reduce((curr, next) => {
  if (next % 2 == 0) curr = [...curr, next * MULTIPLIER];
  return curr;
}, []);
console.log(mapped);

loop_3.js

//Break down
mapped = [];
const isEven = num => num % 2 == 0; // Function returns if even
// Accumulator fun to collect all even number
const accumulator = (records, num) => { 
  // push the current numb at last and create new array
  if (isEven(num)) {
    records = [...records, num * MULTIPLIER];
  }
  return records;
};
mapped = data.reduce(accumulator, []);
console.log(mapped);

null_1.js

class Person {
  constructor(name) {
    this.name = name || null;
  }
}
var deepak = new Person();
// how they check
if (deepak.name == null) {
  console.log("null")
}
console.log(deepak.name && true); // null
deepak = new Person("");
console.log(deepak.name && true); // null
deepak = new Person(false);
console.log(deepak.name && true); // null
deepak = new Person(0);
console.log(deepak.name && true); // null

null_2.js

// Better option
const NO_NAME = Symbol();
class BetterPerson {
  constructor(name) {
    this.name = name || NO_NAME;
  }
  hasName() {
    return this.name !== NO_NAME;
  }
}
deepak = new BetterPerson(0);
console.log(deepak.hasName()); // false
deepak = new BetterPerson("deepak");
console.log(deepak.hasName()); // true

try_1.js

const delay = () =>
  new Promise(r => {
    setTimeout(r, 1000);
  });
const fetchData = async function(url) {
  await delay();
  if (url == "fail") throw "CODE_FAIL";
  if (url == "fatal") throw "CODE_FATAL";
  if (url == "") return "OK";
};
async function main() {
  try {
    const data = await fetchData("fail");
  } catch (e) {
    if (e == "CODE_FAIL") {
      // Show toast message
      console.log(e); // CODE_FAIL
    }
    if (e == "CODE_FATAL") {
      // Show popup message
      console.log(e);
    }
  }
}
main();

try_2.js

// catch function
const onCatchError = e => {
  if (e == "CODE_FAIL") {
    // Show toast message
    console.log(e);
  }
  if (e == "CODE_FATAL") {
    // Show popup message
    console.log(e);
  }
};
const onSomeOtherCatchError = () => {};
async function mainNew() {
  try {
    const data = await fetchData("fail")
      .catch(onCatchError) // CODE_FAIL
      .catch(onSomeOtherCatchError);
  } catch (e) {
    console.log("Something else handle here");
  }
}
mainNew();

us_1.js

const property = Symbol();
class Something {
  constructor() {
    this[property] = "test";
  }
}
var instance = new Something();
console.log(instance["property"]); // undefined
console.log(instance); // Something { [Symbol()]: 'test' }

us_2.js

class Person {
  constructor(nm) {
    this.setName = function (name) {
      nm = name;
    };
    this.getName = function () {
      return nm;
    };
  }
}
const person = new Person("deepak");
console.log(person.getName()); // "deepak"
person.setName("kapeed");
console.log(person.getName()); // "kapeed"
function PersonF(nm) {
  this.setName = function (name) {
    nm = name;
  };
  this.getName = function () {
    return nm;
  };
}
const personf = new PersonF("deepak");
console.log(personf.getName()); // "deepak"
personf.setName("kapeed");
console.log(personf.getName()); // "kapeed"