Javascript Interview and some Math solving.

01| Truthy and Falsy Values;

function total(value){
  if(value){
    return "This is truty value"
 }else{
    return "This is false value"
  }
}
console.log(total(4))

• This is a truthy value. Causes You using a value.

console.log(total(0))
console.log(total("0"))

• Only “0” is the false value. Without “0” all number is a truth value. “Negative” value is a truthy value.
• If the value surrounding a Quotation mark then it is a string. And it is Truty value.

console.log(total(false))
console.log(total("false"))

• If you using a false value then it is a false value.
• If the value surrounding a Quotation mark then it is a string. And it is Truty value.

console.log(total(null))
console.log(total(undefined))
console.log(total(NaN))

• If you using null, undefined, NaN value then this value is a falsy value.

console.log(total("Azizul"))
console.log(total(""))
console.log(total(" "))

• The first console.log is a true value. Causes First console.log value length is not “0”. A similar thing is happened in the third console.log.
• It is not an empty string. This string length is one.
• But The second console.log value.length is “0”.
• Only the empty string is the false value.

let fruits;
console.log(fruits);
  if(name){
    return "This is truty value"
 }else{
    return "This is false value"
  }

console.log(total(4))

• If you declare the fruits variable. But any value is not assigned. Then this value is undefined. And this is falsy value.

The falsey value is “”, NaN, undefined, null, 0 , false, without assinged any value.

02|Null Vs Undefined:

i) Undefined:

let fruits;
console.log(fruits);

• You can declare a variable but not set any value. Then it gives undefined.

function total(num){
  console.log(num)
}
console.log(total(4))

• You can declare a function without return. Then it gives undefined.

function total(x,y){
  return x * y;
}
console.log(total(4))

• You have a function that has two-parameter. But you give one parameter for the result. Then it gives undefined if this function has no default parameter value.

const fruits = {name: "mango", price: 60}
console.log(fruits.quantity)

• If you can read a value in these objects, But this value is not set here. Then this is called undefined.

ii) Null:

• Null is the value this is set by a developer.
• Null is a non-existent and empty value.
• Null is a value that must be assigned.

Undefined is the value that set browser and null is the value that set a developer.

03| Double Equal and Triple Equal:

const number1 = 2;
const number2= "2";
if(number1 == number2){ 
     console.log('condition is true');
  }else{ 
      console.log("condition is not true");
   }
if(number1 === number2){ 
     console.log('condition is true');
  }else{ 
      console.log("condition is not true");
   }

• Here number1 and number2 are variable. When we checked this value is double equal then it checks the value. It is not checking the variable type.
• If you set a string value and check it for double equal then for using double equal the second variable number2 is converting a number and try to match it.
• So the first condition is true.
• On the other hand, the triple equal is checked value and type both.
• So the second condition is false.

const number1 = 0;
const number2= false;
if(number1 == number2){ 
     console.log('condition is true');
  }else{ 
      console.log("condition is not true");
   }

• Then the result is true. Causes actually only “0” is a falsy value.

const number1 = 1;
const number2= true;
if(number1 == number2){ 
     console.log('condition is true');
  }else{ 
      console.log("condition is not true");
   }

• Then the result is true. Causes actually “1” is a truthy value.
• Without 1 any value is using then the condition is false.

04| Map Method:

const fruits = [
 { name: "mango", price: 25},
 { name: "banana", price: 5},
 { name: "jackfruit", price: 50},
]
for(let i = 0 , i < fruits.length i++){
   const food = fruits[i];
   console.log(food.name)
}
const singleFruit = fruits.map(fruit => fruit.name)
console.log(singleFruit)

• The first time in javascript we using the loop(for, while) method.
• After coming ES5 the developer using the map method.
• Map is the alternative method of Loop.
• Map always returns an array.
• In this example, I mapped in fruits array and want all fruits names.
• So the result is [“mango”, “banana”, “jackfruit”]

05| How to hooks work:

function useState(initiateValue){
let value = initiateValue;
 function state(){ 
     return value
  } 
function setState(newValue){
  value = newValue; 
  } 
return [state, setState];
}
// let [food, setFood] = useState([])
// console.log(food());

• This is the useState hook building method.
• At first, we declared a variable that has a parameter. And that assigned into a variable. The variable name is value.
• Then the first function is created that named state and return the parameter value
• THen the second function called setState and take a new parameter. Returns the new parameter.
• At last return two functions.
• And these two functions called outside the function.
• Then console. log food function.
• You get a value that we set by setFood function.

06| Global Scope, Block Scope, Functional Scope or Local Scope:

ler name = "kolmilota"
function total(value){
  console.log(name);
  if(value){
    console.log(name);
    return "This is truty value"
 }else{
    return "This is false value"
  }
 console.log(name);
}
console.log(total(4))

• In this example, we use a let variable outside the function.
• It is called Global scope variable.
• You can excess any place in function or outside the function.

function total(value){
  console.log(name);
  if(value){
    Let name = "kolmilota"
    console.log(name);
    return "This is truty value"
 }else{
    return "This is false value"
  }
 console.log(name);
}
console.log(total(4))

• In this example, we use a let variable inside the if condition in function.
• It is called the Block scope variable.
• You can excess only inside if condition.

function total(value){
  console.log(name);
  if(value){
    var name = "kolmilota"
    console.log(name);
    return "This is truty value"
 }else{
    return "This is false value"
  }
 console.log(name);
}
console.log(total(4))

• When we use the var variable then this variable goes at the top of a function. But the value is not gone.

If you declaired a let or const keyword then it make block scope. It has a specific area. In this example the area is if condition.

If you using a var keyword then it is local or functional scope. You can acccess any place in function this var keyword.

07| Find and Filter Method:

const fruits = [
 { name: "mango", price: 25},
 { name: "banana", price: 5},
 { name: "jackfruit", price: 50},
]
const fruit = fruits.find(fruit => fruit.price > 10);
const fruit = fruits.filter(fruit => fruit.price > 10);

• In this example, we are using the find and filter method.
• In find method check the condition and gives an object.
• The result is { name: ‘mango’, price: 25 }
• On the other hand filter method check the condition and returns an array.
• The result is [ { name: ‘mango’, price: 25 }, { name: ‘jackfruit’, price: 50 } ]

Filter returns in array, and find returns an object.

08| Find max element:

let marks = [42, 3, 4, 23, 44]
let max = marks[0];
for(let i = 0; i < marks.length; i++){
    let element = marks[i]
    if(element > max){
      max = element
    }
 }

• In this example, we declare a variable before for loop.
• We check every element in this array and find the largest element and assign the max variable.

colsole.log(Math.max(...marks))

• In this example, this is the Math.max method. We can easily use this method.

09| Reserve Method:

function stringReversing(string) {
    return string.split("").reverse().join("");
}
stringReversing("Hello");

• In this example, we want to reverse the “hollo” word.
• At first, we split this word then reverse and then join.

10| Define Sum in the Array:

let number= [42, 3, 4, 23, 44]
function getArraySum(number){
  let sum= 0;
 for(let i = 0; i < number.length; i++){
  let element = number[i]
  sum = element + sum;
}
 return sum;
}
console.log(getArraySum(number));

• In this example, we declare a sum variable. Then we start for loop for catching every element in this array.
• Then we added this element to the sum variable.
• We are using the same thing by reduce function using.