Javascript Basics

js-basics.js

// 'use strict';
// a = 1; // throws error due to Strict Mode

console.log('');
console.log('');
console.log('====================');
console.log('Learn JS: Basics');
console.log('====================');
console.log('');
console.log('');

/**
 * Variables and assignments
 *
 *
 */
let a; // declaration - I can be anything
// console.log('a ===>', a);

let b = 'some string'; // declaration with assignment
b = 23;
// console.log('b ===>', b);

const CANNOT_CHANGE_ME_AFTER_ASSIGNMENT = 1; // const declared along with assignment always
// console.log('CANNOT_CHANGE_ME_AFTER_ASSIGNMENT ===>', CANNOT_CHANGE_ME_AFTER_ASSIGNMENT);
// CANNOT_CHANGE_ME_AFTER_ASSIGNMENT = 3;  // throws error

let c; // Declaration and assignment separate
c = 23; // possible due to let. Try this with cosnt
// console.log('c ===>', c);

/**
 * Primitive Data types
 *
 *
 */
// Boolean
const isJavascriptAwesome = true;
// console.log('isJavascriptAwesome ===>', typeof isJavascriptAwesome);

// Null
const iAmNull = null;
// console.log('iAmNull ===>', typeof iAmNull);

// Undefined
const iAmNothing = undefined;
// console.log('iAmNothing ===>', typeof iAmNothing);

// Number
const taskCount = 23;
// console.log('taskCount ===>', typeof taskCount);

// String
const fullName = 'Kannan';
// console.log('fullName ===>', typeof fullName);

// Symbol - Lets learn about this later

// Object
const iAmObject = { x: 23, y: 'ok', z: false, a: null, b: undefined, c: { qwerty: '!!!' } };
// console.log(JSON.stringify(iAmObject));
// console.log('>>', iAmObject.hasOwnProperty('b'));
// console.log('iAmObject ===>', typeof iAmObject);
// console.log('iAmObject.y ===>', typeof iAmObject.y);
// console.log('iAmObject.y ===>', typeof iAmObject.y);
// console.log('iAmObject.hasOwnProperty(y) ===>', iAmObject.hasOwnProperty('y'));

/**
 * Arrays
 *
 *
 */
// Array - Not a primitive and it itself an object
const myArray = [1, 'John', fullName, taskCount, null, undefined, iAmObject, {}];
// console.log('myArray ===>', typeof myArray);
// console.log('length of  ===>', myArray.length);
// console.log('Array.isArray(myArray) ===>', Array.isArray(myArray));

/**
 * Function declarion and invocation
 *
 *
 */
// I will get hosited automatically
function doSomething() {
  // console.log('doSomething is running');
  return 'I did something. Maybe ?';
}
let doSomethingOutput = doSomething();
// console.log('doSomething() ===>', doSomethingOutput);

const doSomethingVariable = function() {
  return 'I still did something. Maybe ?';
};
// console.log('doSomethingVariable() ===>', doSomethingVariable());

const doSomethingArrow = () => {
  return 'I still did something via arrow function.';
};
// console.log('doSomethingArrow() ===>', doSomethingArrow());

/**
 * Function scoping
 *
 *
 */
let myName = 'Outer Scope';
// console.log('myName outside function ===>', myName);
function scopedVariables(myInput1, myInput2) {
  // console.log('myName inside function before re-declaration ===>', myName); // throws error due to scoped let variable

  let myName = 'Inner Scope';
  // myName = 'Changed inside inner scope';
  // console.log('myName inside function ===>', myName, myName2);
  return myName;
}
myName = scopedVariables(2, 'data');
let pop123 = scopedVariables(10, 'myname');
// console.log('myName outside function after ===>', myName);

/**
 * Operators
 *
 *
 */
// unary plus       +
// unary negation	  -
// multiplication	  *
// division	        /
// addition	        +
// subtraction	    -
// assignment	      =
// Reminder         %
// Exponent         **
// Increment        ++
// Decrement        --
// Bitwise          LATER
// Comma            LATER

// Comparison       >   <  >=    <=  ==    === !=   !==

// Conditional      if/else   Ternary

// Logical          &&  ||  !

/**
 * More Functions
 */
function doSomethingProductive() {
  const myWallet = 0;

  let salary = 1000;
  let previousSavings = 200;
  let expenses = 500;

  const bankBalance = myWallet + salary - previousSavings - expenses;

  return bankBalance;
  //   return { bankBalance: bankBalance, myWallet, salary, previousSavings, expenses };
}
// console.log('doSomethingProductive ===>', doSomethingProductive());

/**
 * Loops
 *
 *
 */

let myWallet = 100;
let movieLanguage = 'TAMIL';

while (myWallet > 80) {
  // console.log('I can go for a movie');

  let costForAMovie;

  if (movieLanguage == 'ENG') {
    costForAMovie = 5;
    // console.log('I am watching ENG movie');
  } else {
    costForAMovie = 4;
    // console.log('I am watching Someother lang movie');
  }

  myWallet = myWallet - costForAMovie;
}

// do {
//   // loop body
// } while (condition);

// for (begin; condition; step) {
//   // ... loop body ...
// }

// let xyz = 123;
// console.log(xyz > 300);
// xyz++;
// for (let xyz = 123; xyz < 300; xyz = xyz + 5) {
//   console.log('Each Iteration', xyz);
// }

/**
 * Examples
 *
 *
 */
// console.log('calcSumOfNumbersArray ===>', calcSumOfNumbersArray([5, 2, 10]));

let numbersArray = [5, 2, 10];

function calcSumOfNumbersArray(numArray) {
  // console.log('calcSumOfNumbersArray Function is running with parameters>>>>', numArray);

  let _sum = 0;

  for (let index = 0; index < numArray.length; index++) {
    const element = numArray[index];

    // console.log('Sum before addition', _sum);
    _sum = _sum + element;
    // console.log('Sum after addition', _sum);
  }

  // Write same loop in while, do-while

  return _sum;
}

let myOutput = calcSumOfNumbersArray(numbersArray);
// console.log('>>>>>', myOutput);

console.log('');
console.log('');
console.log('====================');
console.log('END');
console.log('====================');
console.log('');
console.log('');