Javascript Topic

Explain Hoisting in javascript? 🤔

Hoisting is a behavior. Where you can define your variable bottom of moving declarations to the top.
In JavaScript, a variable can be declared after it has been used.

What is Closures in JavaScript? 🤔

A closure is a function having access to the parent scope.

Why we need closer ? 🤔

it is make function have private variable.

Explain with example:

let assume, we create a function that will counter after every click on the button. so first I have declared " x = 0 ". and then create a function with the name " add() ". Whenever I clicked the " add button ". that action access " add()" function. In this function, we can increase our counter easily. But x is a global variable that can access by any other function. We want to declare a function that has its own private variable. For that we use closure.JavaScript supports nested functions. In closure, we declare a variable under the outer function and that variable only accesses the inner function. Code Example: const add = (function () { let counter = 0; return function () {counter += 1; return counter;} })();

What are callbacks? 🤔

Callback is a function.It is passed as an argument to another function.This technique allows a function to call another function.

A callback function can run after another function has finished.

Example of below code:

function myDisplayer(some) {
document.getElementById("demo").innerHTML = some;
}
function myCalculator(num1, num2) {
let sum = num1 + num2;
return sum;
}
let result = myCalculator(5, 5);
myDisplayer(result);

What are high order Functions in javascript? 🤔

Higher-order functions are functions that take other function as arguments or return functions as their result.

For example, the map function on arrays is a higher order function. The map function takes a function as an argument. for example.

const double = n => n * 2

[1, 2, 3, 4].map(double) // [ 2, 4, 6, 8 ]

another example

    var grades = [
    {name: 'John', grade: 8, sex: 'M'},
    {name: 'Sarah', grade: 12, sex: 'F'},
    {name: 'Bob', grade: 16, sex: 'M'},
    {name: 'Johnny', grade: 2, sex: 'M'},
    {name: 'Ethan', grade: 4, sex: 'M'},
    {name: 'Paula', grade: 18, sex: 'F'},
    {name: 'Donald', grade: 5, sex: 'M'},
    {name: 'Jennifer', grade: 13, sex: 'F'},
    {name: 'Courtney', grade: 15, sex: 'F'},
    {name: 'Jane', grade: 9, sex: 'F'}
];

let isBoy = student => student.sex === 'M'

let isGirl = student => student.sex === 'F'

let getBoys = grades => (
    grades.filter(isBoy)
)

let getGirls = grades => (
    grades.filter(isGirl)
)

let average = grades => (
    grades.reduce((acc, curr) => (
        acc + curr.grade
    ), 0) / grades.length
)

let maxGrade = grades => (
    Math.max(...grades.map(student => student.grade))
)

let minGrade = grades => (
    Math.min(...grades.map(student => student.grade))
)

let classroomAverage = average(grades) // 10.2
let boysAverage = average(getBoys(grades)) // 7
let girlsAverage = average(getGirls(grades)) // 13.4
let highestGrade = maxGrade(grades) // 18
let lowestGrade = minGrade(grades) // 2
let highestBoysGrade = maxGrade(getBoys(grades)) // 16
let lowestBoysGrade = minGrade(getBoys(grades)) // 2
let highestGirlsGrade = maxGrade(getGirls(grades)) // 18
let lowestGirlsGrade = minGrade(getGirls(grades)) // 9

What are arrow functions? 🤔

Arrow functions were introduced in ES6.
Arrow functions allow us to write shorter function.
Before use arrow function :

hello = function() {
return "Hello World!";
}

After use arrow function:

hello = () => {
return "Hello World!";
}

What is Destructuring? 🤔

The Destructuring is a way to access array and object value in variable
Let me explain with example

let list = ["rahul","shukla"];

In above code, If i want to access rahul then i do using like this list[0].

let [firstname , lastname] = ["rahul","shukla"];

In Destructuring way, we can access array using "firstname" name variable.
In above code, You can access array using firstname variable and lastname variable.