Functions And Storage Mechanism JavaScript Questions

1. What are the differences between general functions and arrow functions?

Kindly refer to this

2. Explain JavaScript Functions?

A JavaScript Function is a block of code designed to perform a particular task. A JavaScript function is executed when something invokes it (calls it).

We can define the code once, and use it many times. We can use the same code many times with different arguments, to produce different results (We can reuse code ).

Example:

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function myFunction(p1, p2) {

return p1 * p2; // The function returns the product of p1 and p2

}

console.log(myFunction(2, 3)) // Output: 6

console.log(myFunction(5, 8)) // Output: 40

 

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3. What are the different types of JavaScript Functions?

• Function declaration (regular function)
• Function expression
• Shorthand method definition
• Arrow function
• Generator function

4. What is a Factory Function?

A Factory function is any function that returns a new object for every function call. The Function name should follow the camelCase naming convention.

Syntax:

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function functionName(parameter1, parameter2) {

return {

property1: parameter1,

property2: parameter2,

}

}

let myObject = functionName(arg1, arg2);

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function createCar(color, brand) {

return {

color: color,

brand: brand,

start: function() {

console.log("started");

}

};

}

let car1 = createCar("blue", "Audi");

let car2 = createCar("red", "Tata");

let car3 = createCar("green", "BMW");

console.log(car1); // Output: Object { color: "blue", brand: "Audi", start: ƒ() }

console.log(car2); // Output: Object { color: "red", brand: "Tata", start: ƒ() }

console.log(car3); // Output: Object { color: "green", brand: "BMW", start: ƒ() }

 

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5. What is a Constructor Function?

The Constructor Function is used to create Objects.

It is a regular function that returns a new object on calling with the

new

operator. The created new object is called an Instance.

Syntax:

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function FunctionName(parameter1, parameter2, ...) {

this.property1 = parameter1;

this.property2 = parameter2;

...

...

}

let myObject = new FunctionName(arg1, arg2, ...)

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When a function is called with the

new

operator, it does the following steps:

• Creates an empty object and assigns it to 
  this
• Return 
  this

Example:

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function Car(color, brand) {

this.color = color;

this.brand = brand;

this.start = function () {

console.log("started");

};

}

let car1 = new Car("blue", "Audi");

console.log(car1); // Car { }

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Note

The Function name should follow the PascalCase naming convention.

6. What function is called when two functions have the same name?

The last function is called.

When we define the multiple functions with the same name, then the last defined one will be called. It is called Function Overriding.

JavaScript supports Function Overriding.

7. What is a regular function?

A Regular function is nothing but the Function Declaration.

It is defined by a

function

keyword, followed by a function name, a list of parameters in a pair of parenthesis

(param1, ..., paramN)

and a pair of curly braces

{...}

that contains the function body.

Example:

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function getArrayLength(array) {

return array.length;

}

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8. Name any four client-side storages?

Client-Side Data Storage is storing the data on the client (user's machine).

• Local Storage
• Session Storage
• Cookies
• IndexedDB and many more.

9. What is the size of localStorage?

LocalStorage is limited to about 5MB and can contain only strings.

10. What is local storage and its methods?

The Local Storage allows web applications to store data locally within the user's browser. It is a Storage Object. Data can be stored in the form of key-value pairs.

Methods:

setItem(): The

setItem

method can be used for storing data in the Local Storage.

Syntax:

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localStorage.setItem("Key", "Value");

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getItem(): The

getItem

method can be used for getting data from the Local Storage.

Syntax:

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localStorage.getItem("Key");

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removeItem(): The

removeItem

method can be used for removing the specified Storage Object item from the Local Storage.

Syntax:

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localStorage.removeItem("Key");

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11. Whether the Local Storage values will be deleted if we clear the cache in Browser?

No, the Local Storage values won't be deleted if we clear the cache.

Local Storage values will be deleted,

• When removed the particular key value using the 
  localStorage.removeItem
   method
• When removed the whole Local Storage values using the 
  localStorage.clear
   method
• When cleared the recent history with the cookies from start time in Browser.

12. How do you know the Cookie has expired?

While using the

js-cookie

third-party package, we use

Cookies.get

method to access the cookie.

We can know the Cookie has expired, if the

Cookies.get

methods returns

undefined

.

Example:

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const token = Cookies.get("jwt_token"); // Assume that there is was a Cookie set with the key "jwt_token" with value the 1234

if (token === undefined) {

console.log("Cookie is expired");

}

 

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13. How do you find the present date and time?

We can find the present date and time by using

new Date()

method.

We can create a date object without passing any arguments to the

new Date()

method.

Example:

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let now = new Date();

console.log(now); // Output: Tue Feb 24 2021 19:10:29 GMT+0530 (India Standard Time) { }

 

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Here, the

new Date()

method creates a new date object with the present date and local time.

14. Name some of the built-in methods in JavaScript?

some of the built-in methods in JavaScript:

Name	Description
ceil()	Returns the smallest integer that is greater than or equal to the given number
concat()	Combines two strings and returns the newer string
constructor()	Returns the function that created the corresponding instance of the object
Date()	Returns the present date and time
pop()	Removes and returns the last element from an array
slice()	Returns the selected elements in an array, as a new array.

15. What is an arrow function?

An Arrow function is a simple and concise syntax for defining functions.

It is an alternative to a function expression.

Syntax:

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let sum = (param1, param2, …) => {

// statement(s)

};

sum()

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Example:

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let sum = (a, b) => {

let result = a + b;

return result;

};

console.log(sum(4, 3)); // Output: 7

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16. What are the uses of Arrow Functions?

An Arrow function is a simple and concise syntax for defining functions.

• It is an alternative to a function expression.
• It inherits 
  this
   from the context in which the code is defined.
• The 
  return
   statement and curly braces are not required for simple expressions.
• If there is only one parameter, then parentheses are not required.