Variables

Thursday, June 11, 2020

Course Link

1. Basic JavaScript

How to comment?

 //exactitude
 /* hi, 
 how is the novel?*/

2. Seven Data types

undefined: declared variables without values
null
symbol
boolean
string: immutable
number
object

3. Numeric variable

Store a value in a variable
```
var q = 1.1
```

Value Operator

Increment and decrement

i = 19
i++ 
// is the equivalent of i = i + 1
  
i-- 
// is the equivalent of i = i - 1

Remainder operator %

17 % 2 = 1 // 17 is odd
18 % 2 = 0 // 18 is even

Compound assignment With augmented addition, substraction, multiplication and devision

var a = 90;
a += 9; // this is equal to a = a + 9;
a -= 9; // this is equal to a = a -9;
a *= 9; // this is eqaul to a = a * 9;
a /= 9; // this is equal to a = a / 9;

4. String variable

var p = "Mauriat";

# Escaping Literal Quotes in Strings
var p = "Mauriat said, \"I worked as an arranger for other artists \".";

# Quoting Strings with Single Quotes
var myStr = '<a href="http://www.example.com" target="_blank">Link</a>';

# Escape Sequences in Strings
var myStr = 'FirstLine\n\t\\SecondLine\nThirdLine'; // Change this line

Escaping characters

Code	Output
-'	single quote
-"	double quote
-\	backslash
-\n	newline
-\r	carriage return
-\t	tab
-\b	word boundary
-\f	form feed

Concatenating Strings with plus operator, plus equals operator

var myWords = "I hear " + "you say: "; 

var myWords += "It's gonna be OK";

Find the lenth of a String

var myWordseLength = myWords.length;

Use bracket notation to find the first/last character in a string

var firstLetter = myWords[0];
var lastLetter = myWords[myWords.length-1];
var thirdToLastLetter = myWords[myWords.length - 3];

5. Array variable

Store multiple values in one variable using JavaScript arrays

   var myArray = ["a",1]

Multidimensional array: nest one array within another array

   var myArray = [["a",1],["b",2]]

Access array data with indexes

   var myData = myArray[0]

   # Access array of arrays 
   var arr = [
     [1,2,3],
     [4,5,6],
     [7,8,9],
     [[10,11,12], 13, 14]
     ];
   arr[3]; // equals [[10,11,12], 13, 14]
   arr[3][0]; // equals [10,11,12]
   arr[3][0][1]; // equals 11

Modify array data with indexes

  var ourArray = [50,40,30];
  ourArray[0] = 15; // equals [15,40,30]

Manipulate arrays with push()

var arr1 = [1,2,3];
arr1.push(4);
// arr1 is now [1,2,3,4]

var arr2 = ["Stimpson", "J", "cat"];
arr2.push(["happy", "joy"]);
// arr2 now equals ["Stimpson", "J", "cat", ["happy", "joy"]]

Remove the first element from an array

var ourArray = ["Stimpson", "J", ["cat"]];
var removedFromOurArray = ourArray.shift();
// removedFromOurArray now equals "Stimpson" and ourArray now equals ["J", ["cat"]]

Remove the last element from an array

var threeArr = [1, 4, 6];
var oneDown = threeArr.pop();
console.log(oneDown); // Returns 6
console.log(threeArr); // Returns [1, 4]

Add an element to the beginning of an array

var ourArray = ["Stimpson", "dog"];
ourArray.shift(); // ourArray now equals ["dog"]
ourArray.unshift("Happy");
// ourArray now equals ["Happy", "dog"]

6. Boolean

Boolean values are never written with quotes.

The strings “true” and “false” are not Boolean and have no special meaning in JavaScript.

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