Javascript Basic

Global var and Local var
That’s important !! need to understand diffrent of three examples.

// example 1
let TestValue = "Global";
function ChangeValue(){
	let TestVaule = "Local";
}
document.write(TestValue);
// the answer is : Global

// example 2
let TestValue = "Global";
function ChangeValue(){
	let TestVaule = "Local";
  document.write(TestValue);
}
// the answer is : Local

// example 3
let TestValue = "Global";
function ChangeValue(){
	TestVaule = "Local";
}
document.write(TestValue);
// the answer is : Local

Function as a value
Function is object in javascript. that means function can be value in javascript.

function a(){} // it means var a  = function(){}
  
a = {
  b:function(){ // b is methods of object a
  }
}
// object a has key b and value function

function cal(func num){
  return func(num)
}
function increase(num){
  return num+1
}
function decrease(num){
  return num-1
}
alert(cal(increase,1));
alert(cal(decrease,1));

Callback

function sortNumber(a,b){
  return b-a;
}
var numbers = [20,10,9,8,7,6,5,4,3,2,1];
alert(numbers.sort(sortNumber)); // array [20,10,9,8,7,6,5,4,3,2,1]
// sortNumber is callback function.

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Javascript Basic

Closure

A closure is the combination of a function and the lexical environment within which that function was declared.

//example
function outter(){
  var title = 'coding everybody';
  function inner(){
    alert(title);
  }
  inner();
}
// result : coding everybody
// as you can see, inner function can access to the var title 
// even though title is located outside of the function. That's a Closure

Private variable

function factory_movie(title){
  return {
    get_title : function (){
      return title;
    }
    set_title : function(_title){
        if(typeof _title === 'string'){
            title = _title;
        }else{
            alert('subject should be string type');
        }
    }
  }
}
ghost = factory_movie('Ghost in the shell');
matrix = factory_movie('Matrix');

alert(ghost.get_title); // Ghost in the shell
alert(matrix.get_title); // Matrix

Parameter and Arguments

function sum(){
  var i, _sum = 0;
  for(i=0; i<arguments.length; i++){ 
    // even though there is no parameter but js can access to arguments
    document.write(i+' : '+arguments[i]+'<br />');
    _sum += arguments[i];
  }
  return _sum;
}
document.write('result : ' + sum(1,2,3,4));

Apply

The apply() method calls a function with a given this value, and arguments provided as an array (or an array-like object).

o1 = {val:1, val2:2, val3:3}
o2 = {v1:10, v2:50, v3:100, v4:25}
function sum(){
  var _sum = 0;
  for(name in this){
    _sum += this[name];
  }
  return _sum;
}
alert(sum.apply(o1)) // 6
alert(sum.apply(o2)) // 185

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Day 0: Hello, World! Problem : Hello, World
My code :

function greeting(parameterVariable) {
    // This line prints 'Hello, World!' to the console:
    console.log('Hello, World!');

    // Write a line of code that prints parameterVariable to stdout using console.log:
    console.log(parameterVariable);
}

Day 0: Data Types Problem : Data Types
My code :

function performOperation(secondInteger, secondDecimal, secondString) {
    // Declare a variable named 'firstInteger' and initialize with integer value 4.
    const firstInteger = 4;
    
    // Declare a variable named 'firstDecimal' and initialize with floating-point value 4.0.
    const firstDecimal = 4.0;
    
    // Declare a variable named 'firstString' and initialize with the string "HackerRank".
    const firstString = 'HackerRank ';

    console.log(parseInt(firstInteger) + parseInt(secondInteger));
    // Write code that uses console.log to print the sum of the 'firstInteger' and 'secondInteger' (converted to a Number type) on a new line.
    
    console.log(parseFloat(firstDecimal) + parseFloat(secondDecimal));
    // Write code that uses console.log to print the sum of 'firstDecimal' and 'secondDecimal' (converted to a Number type) on a new line.
    
    console.log(firstString + secondString);
    // Write code that uses console.log to print the concatenation of 'firstString' and 'secondString' on a new line. The variable 'firstString' must be printed first.

Day 1: Arithmetic Operators Problem : Arithmetic Operators
My code :

function getArea(length, width) {
    let area;
    area = length * width;
    
    // Write your code here
    
    return area;
}

/**
*   Calculate the perimeter of a rectangle.
*	
*	length: The length of the rectangle.
*   width: The width of the rectangle.
*   
*	Return a number denoting the perimeter of a rectangle.
**/
function getPerimeter(length, width) {
    let perimeter;
    perimeter = 2 * (length + width);
    // Write your code here
    
    return perimeter;
}

Day 1: Functions Problem : Functions
My code :

/*
 * Create the function factorial here
 */
function factorial(n) {
    var result = 1;
    for (var i=1; i<(n+1); i++) {
        result *= i;
    }
    return result;
}

Day 1: Let and Const Problem : Let and Const
My code :

function main() {
    const PI = Math.PI;
    // Write your code here. Read input using 'readLine()' and print output using 'console.log()'.
    const r = readLine();

    console.log(PI * r * r);
    // Print the area of the circle:
    console.log(2 * r * PI);
    // Print the perimeter of the circle:

Day 2: Conditional Statements: If-Else Problem : Conditional Statements: If-Else
My code :

Day 2: Conditional Statements: Switch Problem : Conditional Statements: Switch
My code :

Day 2: LoopsProblem : Loops
My code :

Day 3: Arrays Problem : Arrays
My code :

Day 3: Try, Catch, and Finally Problem : Try, Catch, and Finally
My code :

Day 3: Throw Problem : Throw
My code :

Day 4: Create a Rectangle Object Problem : Create a Rectangle Object
My code :

Day 4: Count Objects Problem : Count Objects
My code :

Day 4: Classes Problem : Classes
My code :

Day 5: Inheritance Problem : Inheritance
My code :

Day 5: Template Literals Problem : Template Literals
My code :

Day 5: Arrow Functions Problem : Arrow Functions
My code :

Day 6: Bitwise Operators Problem : Bitwise Operators
My code :

Day 6: JavaScript Dates Problem : JavaScript Dates
My code :

Day 7: Regular Expressions I Problem : Regular Expressions I
My code :

Day 7: Regular Expressions II Problem : Regular Expressions II
My code :

Day 7: Regular Expressions III Problem : Regular Expressions III
My code :

Day 8: Create a Button Problem : Create a Button
My code :

Day 8: Buttons Container Problem : Buttons Container
My code :

Day 9: Binary Calculator Problem : Binary Calculator
My code :

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