Learning JavaScript

• Getting Started
• JS in the Web Browser
• console.log()
• Variables
• Data Types
• String Concatenation
• Operators
• Conditional Statements

Console.log()

This is the method used to output text onto the console (not the screen)

console.log("Hello World!"); //semi-colons are optional

// you can format the code in Console bu using `%c`
console.log("%c Hi There!", "color:blue; font-size:48px;");

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Variables

There are (3) keywords to declare variables:

• var the most lenient type of Variables.
• let included in ES6 somewhat strict type of variables
• const used to create constant (unmodifiable variables)

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Variables

There are (3) ways to create a variable in JS:

• var: creates a somewhat global variable.
• let: creates a scoped variable
• const: creates a CONSTANT variable

/*  Using let */
let _var = 67;

function myFunc() {
  // this variables is only accessible inside the function.
  let _var = 100;
}

/* Using const */
// this variable can not be 'reassigned'
const _constant = "I am unchangeable";

/* Using var */
// This variable can be accessed EVERYWHERE in the code
var _anotherVar = null;

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Primitive & Non-Primitive Data Types

Primitive: Data types that are built-in to the language. Examples are:

// nn bb ss u
let _null = null;
let _num = 34;
let _bool = true;
let _bigInt = 456n;
let _string = "ARK";
let _symbol = Symbol("I am a Symbol!");
let _undef = undefined;

Non-Primitive: Data Types that are user-defined. Examples are: Objects.

let _myObj = {
  name: "ARK",
  age: 19,
  skinColor: "Dark Orange",
};

In the above code an object is assigned to the variable named '_myObj'. The object contains key-value pair this means every properties of object can be accessed by a specific key. There are several ways to access the properties of an object

Using dot (.) operator:

let name = _myObj.name;
console.log(name);

// output: "ARK"

Using Object Literal:

let age = _myObj["age"];
console.log(age);

// Output: 19

String Concatenation

Concatenation is the process used to combine two or more string together. There are severel ways of concatenating String in JavaScript

1. using the concat method
2. using the + operator
3. using the , operator

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Method 1:

str1 = "My";
str2 = "String";

// combines the two existing strings
str3 = str1.concat(str2);

// MyString

Method 2:

str1 = "My name is";
str2 = "ARK";

console.log(str1 + str2);

// My name isARK

Method 3:

str1 = "My name is";
str2 = "ARK";

console.log(str1, str2);

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Loops

There are many types of loops in JS:

• For loop

for (let i = 0; i < 11; i++) {
  console.log(i);
}

• For-in loop: Used for printing the values of an object

// An object literal assigned to a variable named 'Obj'
let obj = {
  name: "ARK",
  age: 19,
  isMale: true,
};

for (let keys in obj) {
  console.log(`${keys}: ${obj[keys]}`);
}

/*
Output:
    name: ARK
    age: 19
    isMale: true 
*/

• For-of loop: used to iterate over the elements of an Array

// Array of fruits (string).
let arr = ["lemon", "banana", "apple", "strawberry"];
for (let item of arr) {
  console.log(`${item}`);
}
/* 
Output: 
    lemon
    banana
    apple
    strawberry 
*/

• While Loop

let i = 0;
while (true) {
  console.log(++i);
}
// Output: 1, 2, 3...

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String Methods

let name = "ark";
console.log(name.length); // tells the number of charachters present in the string
console.log(name.toUpperCase()); // converts the string to UPPERCASE
console.log(name.toLowerCase()); // converts the string to lowercase
console.log(name.replace("a", "s")); // replaces 'a' in string 'ark' with 's'. Output: 'srk'

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Arrays

A data type that is used to store collection of data types.

let arr = ["banana", 70, 3.142, true];

Methods of Array

arr.push("ARK"); // adds new element at the end
arr.pop(); // removes element from the end
arr.shift(); // removes element from the front
arr.unshift(); // adds element from the front

Turnary Operator

Syntax:

condition ? if_true : if_false;

Example:

let result = 1 > 2 ? "1 is greater than 2" : "1 is NOT greater than 2";
console.log(result);

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