Learn javaScript Basics- Day 4

1. HTML: html used for describing content
2. CSS: css used for describing presentation of the content
3. JavaScript: javascript used for describing behaviours

Run JavaScript in VS Code

• node filename.js

or, 

• click run button in VS code
• create a launch.json file
• select node.js preview

html and css are not programming language. JavaScript is a programming language. 

Programming is a set of instruction (which is written by programmer) that telling a computer what to do.  

 What does the alert() function do?

• The alert function opens up a pop-up box with whatever text you pass to it.

What does prompt() funtion do?

• The prompt function opens up a pop up box with a text field that allows the user to type an answer, which it will then return to code.

Primitive values are hardcoded and therefore cannot be changed. if a=10, you can change the value of x you can not change 10

Javascript data types

• Numbers
• String
• booleans
• null
• undefined
• object
• function

1. Numbers: JavaScript only has one type for numbers: 64 bit floating point values. It includes  two additional values: infinity and NaN (not a number)
2. String:  Strings are used to represent text in JavaScript. To create a string in JavaScript, you enclose characters with either single or double quote.
3. Booleans: Booleans data types have two values: true and false. 
4. Object: In JavaScript, objects are king. If you understand objects, you understand JavaScript -w3schools. 
5. null: null is a primitive values and is treated as falsy for boolean operations.
6. undefined: undefined means a variable declared, but no value has been assigned
7. function

typeof is a built in function that help us to see the data type of any value. 

• typeof(15) 
• typeof "fruits"
• typeof prompt
• typeof 20/"fruits"

Interview Question: 

1. What are the seven data types in javascript?

Numbers, string, boolean, null, object, function, undefined

2. What is the difference between null and undefined? 

undefined means a variable declared, but no value has been assigned. null is a primitive values and is treated as falsy for boolean operations.

3. Enter an expression in the console that evaluates to NaN. 

parseInt("Hello");

Numbers, Arithmetic Operators, Comparators

Numbers: number is one type of data type in javascript. number needs to perform arithmetic operations. 

Arthmectic Operators:  Arithmetic operators are things like: +, -, *, and /. They're used to compute values.  There are five arithmetic operators in JavaScript,

• +
• -
• *
• /
• %

Comperators: Comparators are used to compare values and they return either true or false. 

• > (greater than)
• < (less than)
• ==
• ===
• !=
• !==
• >= greater or equal
• <= less or equal

Operator precedence: This tells code the order in which operations should be performed fast. 

  

Interview Question

1. How modulas operator perform? 

if a = 35%10, then a is store 5 which which is the remainder after dividing 35 by 10.

2. What is the order of arithmetic operations in JavaScript? 

PEMDES - parenthesis(bracket), exponent(3**4 = 81), Multiplication, Division, Addition, Subtraction

String 

String is collection of charecter that is used to reperesent a text. Use "" to enclose the text. Example: myName="Mojnu" 

Length Property

var charecterCount = "90 Day Challenge for Get a Job";

console.log(charecterCount.length);

String Concatenation

• String concatenation is combining two or more strings into a single string. For example: 

var addTwoWord = "I Love" + "My Mother";

console.log(addTwoWord)

String Comparisons 

var checkTwoStingEqual = "I Love" !== "My Mother";

console.log(checkTwoStingEqual)

Interveiw Question

1. What is string concatenation? 

2. What happen when Concatenate a string + number? 

var stringPlusNumber = 90 + " Day";

console.log(stringPlusNumber)

3. Escape charecter? 

• \t tab 
• \n new line 
• \r carriage return
• \' start /end of string
• \\ backslash
• \uHHHH

Variables

• A variable is a named reference to a location in memory for storing data.
• javascript is untyped, it means that you don't need to declare it's type.
• to create a variable you can simply type => var varName = value;
• variable name can not begin with number. Ex: 90day is not correct to declare a variable
• can not use special charecter in variable name without $ and -
• can not have space in variable name
• follow camel case when you declare a variable

Interview Question:

1. Declare a variable?

var daysRemain = 86;

2. Find the length?

var quote = "My name is Mojnu. I am a full stack web developer. I challenge myself in september 1 to get a job in 90 day" console.log(quote.length);

3. Give an Example of Increment or decrement?

 var days = 90; days++;  

Conditional Statements 

var days= 4;

if(days == 90) {

console.log("The End Game");

}

else if(days == 0) {

console.log("The Game Start");

}

else {

console.log("It's day 4, try hard mama");

} 

 

Truthy or falsy condition

• if("hello") - true condition
• if("") - false condition
• if(false) - falsy
• if(0) - falsy
• if(null) - falsy
• if(undefined) - falsy
• if(NaN) - falsy

Loops in Programming Language 

• Loops can execute a block of code a number of times until complete the process

For Loop: 

for (var i = 1; i < 11; i++) {

   console.log(i);

}

//output: 1 2 3 4 5 6 7 8 9 10

While Loop: 

var days = 10;

while (days > 4) {

   console.log(days);

days--;

}

//output: 10 9 8 7 6 5

Array

• JavaScript arrays are used to store multiple values in a single variable. -w3Schools 
• const cars = ["Saab", "Volvo", "BMW"]; //declare an Array
• To access the items of an array, an indexer must be used: console.log(cars[2]) //result: BMW
• modify the tems in an array like this: cars[2] = "Toyota";

concat: join one or more arrays. See the example below,

    const addCars = ["Ford Motor", "Daimler", "Volkswagen"];

    const totalCars = cars.concat(addCars);

    //result totalCars = ["Saab", "Volvo", "BMW", "Ford Motor", "Daimler", "Volkswagen"]

indexOf: var flowers = ["rose" , "lily", "tulip"];

console.log(flowers.indexOf("lily"));
//result: 1
console.log(flowers.indexOf("bely"));
//result: -1 because bely flower is not in flowers array.

• indexOf return -1 if the items not found in the array

lastIndexOf: 

• lastIndexOf searches the item from the last in the array. Ex: lastIndexOf("tulip"); //output: 0

pop: 

• remove item from to the end of array
• example: https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/pop.js

push:

• add new item to the end
• example: https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/push.js

shift: 

• remove first item from array
• Example: https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/shift.js

unshift:

• add item to the first index of the array
• https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/unshift.js

slice:

• slice return the new array which is a part of an existing array
• https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/slice.js

splice:

• splice add or removes item from an array
• https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/splice.js

sort:

• sort return the new array by alphabetical order
• example: https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/sort.js

reverse:

• reverse an array
• example: https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/reverse.js

toSring:

• creates string from the item of the array
• https://github.com/coderMojnu/90DaysChallenge/blob/master/Day5/arrayAndFunction-day5/toString.js