Higher Order Function | javascript interview series

Summary

In this video, the host delves into the concept of higher-order functions in JavaScript, emphasizing their importance in interviews. He explains that higher-order functions either take a function as an argument or return a function. The video highlights practical examples, such as setTimeout and array filter methods, to illustrate the concept. Additionally, the host advises candidates to share personal experiences and project implementations to make their answers more engaging and impressive to interviewers. The goal is to transform the interview into a discussion, showcasing not just knowledge, but practical understanding and application of higher-order functions.

Takeaways

• 📚 A higher order function in JavaScript is defined as a function that takes another function as an argument or returns a function.
• 🔍 The candidate's eagerness to answer the definition from MDN is noted, but interviewers seek a deeper understanding and personal experience with higher order functions.
• 💡 The script suggests starting explanations with code examples to illustrate the concept of higher order functions, such as using `setTimeout`.
• 👨‍🏫 The importance of turning an interview question into a discussion is emphasized, sharing personal stories and experiences with higher order functions.
• 🔑 The script uses `filter` as an example of a higher order function, explaining how it processes arrays based on a provided function.
• 🛠️ The benefits of higher order functions include writing less code, improving readability, and making code more maintainable.
• 📈 The script provides an example of creating an `asyncHandler` to streamline error handling and database interactions in a project.
• 🔄 The `asyncHandler` example demonstrates how functions can be treated as variables, passed around, and composed to create more complex functionality.
• 📝 The candidate is encouraged to share specific use cases from their own projects to showcase their understanding and application of higher order functions.
• 🚀 The script concludes by advising candidates to focus on storytelling and personal experiences with higher order functions to impress interviewers.
• 👋 The video ends with an invitation to subscribe for more interview tips and to stay tuned for the next video in the series.

Q & A

What is the definition of a higher order function according to the video?

A higher order function is a function that takes another function as an argument or returns a function.

Why is it important to discuss higher order functions in a JavaScript interview?

Higher order functions are a common practice in JavaScript and discussing them can demonstrate a candidate's understanding and practical experience with functional programming concepts.

What is the first example of a higher order function given in the video?

The first example given is 'setTimeout', which is a function that takes another function as an argument to execute after a specified delay.

How does the video suggest explaining the concept of higher order functions during an interview?

The video suggests explaining higher order functions with code examples, starting with basic examples like 'setTimeout', and then moving on to more complex examples like using 'filter' and 'reduce'.

What is the advantage of using higher order functions in coding?

Higher order functions allow for writing less code that is more readable, maintainable, and can be easily reused and modified.

Can you provide an example of how to use the 'filter' method as a higher order function?

The 'filter' method can be used to process an array, for example, to filter out salaries above a certain value by providing a function that checks if each element meets the condition.

What is the purpose of creating an asyncHandler in the context of the video?

The asyncHandler is created to simplify error handling and to avoid repetitive code when interacting with databases, making the code more efficient and less prone to errors.

How does the video suggest using higher order functions to improve the asyncHandler example?

By treating functions as variables that can be passed and returned, the asyncHandler can wrap any function in a try-catch block and convert it to an async function, making it more versatile and error-resistant.

What is the significance of the 'useHandler' function in the asyncHandler example?

The 'useHandler' function is significant because it demonstrates how to pass a function as an argument to another function, which then processes it within an async context and error handling, showcasing the power of higher order functions.

How can a candidate impress interviewers with their understanding of higher order functions?

A candidate can impress interviewers by not only defining higher order functions but also by narrating a story of their first encounter with the concept, explaining how they implemented it in projects, and discussing its advantages.

What is the final advice given in the video for candidates preparing for a JavaScript interview?

The final advice is to focus on understanding and being able to explain higher order functions with practical examples and use cases, which can demonstrate a well-versed programming skill set.

Outlines

00:00

📘 Understanding Higher Order Functions in JavaScript

This paragraph delves into the concept of higher order functions in JavaScript, which are functions that either take another function as an argument or return a function. The speaker emphasizes the importance of not just knowing the definition from MDN, but also being able to discuss the first time the concept clicked and how it has been implemented in practice. The paragraph provides examples like 'setTimeout' to illustrate higher order functions and encourages interviewees to share a story that demonstrates their understanding and use of the concept, rather than just repeating definitions.

05:00

🔍 Practical Applications of Higher Order Functions

The speaker provides practical examples of higher order functions, such as the 'filter' method in JavaScript, which processes arrays based on a provided function. The paragraph explains how higher order functions can lead to more concise, readable, and maintainable code. It also discusses the advantages of using higher order functions, like chaining 'filter' methods and the ability to pass functions as parameters to other functions, as demonstrated in the creation of an async handler for database interactions. The paragraph encourages interviewees to share their own experiences using higher order functions in projects to impress interviewers.

10:02

🚀 Enhancing Code with Higher Order Functions

This paragraph continues the discussion on higher order functions, focusing on how they can be used to create more efficient and error-free code. The speaker uses the example of an async handler that wraps database calls in try-catch blocks to prevent errors from propagating. The paragraph highlights the beauty of higher order functions in allowing developers to pass functions as variables and return them from other functions, leading to cleaner and more modular code. It concludes with advice for interviewees to share specific use cases from their projects to demonstrate their proficiency with higher order functions.

Keywords

💡Higher Order Function

A higher order function is a function that takes another function as an argument, or returns a function as its result. In the context of the video, it is a fundamental concept in JavaScript that allows for more dynamic and reusable code. The script uses higher order functions like `setTimeout` and `filter` to illustrate how they can be used to create more concise and maintainable code.

💡MDN

MDN stands for Mozilla Developer Network, which is a comprehensive resource for web developers. In the video, the speaker refers to MDN to provide the standard definition of a higher order function, emphasizing the importance of understanding and being able to explain industry-standard terms.

💡Interview

The video script revolves around preparing for a JavaScript interview, focusing on how to answer questions about higher order functions effectively. The term 'interview' is used to set the context of the discussion, highlighting the practical application of theoretical knowledge in a professional setting.

💡setTimeout

In JavaScript, `setTimeout` is a higher order function used to schedule code to be executed after a specified delay. The video uses `setTimeout` as an example to demonstrate how higher order functions can accept a function as an argument, thereby showcasing its use in real-world coding scenarios.

💡Filter

The `filter` method in JavaScript is a higher order function that creates a new array with all elements that pass a test implemented by the provided function. The script explains how `filter` can be used to process arrays, emphasizing the advantage of higher order functions in writing less and more readable code.

💡Closure

A closure in JavaScript refers to the combination of a function and the lexical environment within which that function was declared. The video mentions closures when discussing the behavior of functions passed to `setTimeout`, indicating the importance of understanding how functions maintain access to their surrounding scope.

💡Front-end Developer

A front-end developer is a programmer who specializes in the client-side of applications, focusing on user interface and user experience. The script mentions front-end developers to highlight that higher order functions are a common practice across different roles in web development.

💡Back-end Developer

A back-end developer is responsible for the server-side of applications, managing databases, server logic, and application interactions. The video script uses the term to emphasize that higher order functions are relevant to developers working in both front-end and back-end roles.

💡Async Handler

An async handler is a function designed to manage asynchronous operations, often used in JavaScript to handle promises and errors. The video script discusses creating an async handler as an example of a practical use case for higher order functions, demonstrating how they can simplify error handling in database interactions.

💡Express

Express is a popular web application framework for Node.js, often used for building web applications and APIs. The script refers to Express when explaining how higher order functions can be used in middleware to create clean and efficient server-side code.

💡Try Catch

In JavaScript, 'try' and 'catch' blocks are used for error handling, allowing developers to catch and handle errors in asynchronous code. The video script mentions 'try catch' in the context of creating an async handler, illustrating how higher order functions can be used to streamline error handling in complex applications.

Highlights

Introduction to the concept of higher order functions in JavaScript.

The importance of not just knowing the definition but also being able to discuss and demonstrate higher order functions.

Definition of higher order functions according to MDN: functions that take other functions as arguments or return a function.

The need to share a personal story or experience with higher order functions to impress interviewers.

Explanation of how to use higher order functions with code examples.

The use of setTimeout as an example of a higher order function.

Demonstration of how functions can be treated as variables in higher order functions.

The advantage of using higher order functions for writing less and more readable code.

The use of filter as a higher order function to process arrays.

Chaining higher order functions for more complex logics.

The practical application of higher order functions in a project for async handling.

Creating a syncHandler utility function to reduce repetitive code.

The process of converting a regular function into a higher order function step by step.

Incorporating higher order functions into middleware for error handling in Express.

Wrapping functions with try-catch for robust error handling using higher order functions.

The importance of understanding and being able to explain the practical use of higher order functions in interviews.

Encouragement to narrate a story with higher order functions to stand out in interviews.

Advice for those who have not built anything with higher order functions to prepare well for interviews.

Transcripts

hey there everyone they share back again

with another video and in this video we

are continuing our JavaScript interview

series yes I kind of got laid into it

but here is another question for you

what is a higher order function the

moment a candidate gets a question that

what is a higher order function he just

get started a higher order function is a

function that takes function as a

parameter auditor I really understand

that you are very eager to answer the

definition which is given on the mdn and

to be honest let me just show you that

what it is so if you go up here onto the

mdn docs you'll find that there is a

note that what higher order function

should be considered or what that is if

you go up here it says a function that

returns a function or takes other

function as argument as is considered as

a higher order function a perfectly well

definition but the reason why you are

not able to impress the interviewers in

this question is because you are just

answering the question which is a good

thing but the best interviews are the

ones which eventually get converts into

a discussion the interviewer also knows

that this is the definition of higher

order function but his intention mostly

are is to get to know that when was the

first time it clicked that it is a

higher order function

and when did the first time you actually

implemented or used it whether you're

coming up from a front-end developer

back-end developer this is such a common

practice that's why it appears so many

times in the interview so you should

really portray down a story which

obviously explains the topic just stay

on the high order function don't go into

the event loops and all that thing it's

really good that you know about them you

have watched a lot of videos on YouTube

about it but try to stick on to the

higher function let me give you a

definition not just the definition a way

of explanation of how you should be

doing it as what is a high order

function for the interview perspective

so this is a higher order function you

should really start explaining such

things with the code so we have seen

functions like this so there is a

function let's just say there is a

function known as salary which takes a

number whatever the number is and it

simply go ahead and simply say that

number multiplied by 0.7 so it cuts down

the taxes and only gives you 70 percent

this is a perfectly fine function in but

it cannot be considered as higher order

function simple reason this is taking a

number and giving me a value by

processing it it might take an ID and

might just query the database and give

us the value so what is a higher order

function according to the definition or

according to the definition made by

programmers it should either take a

value which is a function or returns a

value which is a function so the example

should be given up started by the very

first and the basic that if higher order

function you want to talk about set

timeout is one of the higher order

function because it it just verifies all

the check marks which is there so set

timeout is a function or an API

which uh you cannot actually work with

it without being a high order function

because you are telling the set timeout

that hey wait for x amount of time and

then do this task for me and task is

always a set of instruction that you are

providing him so obviously you have to

provide a function to it and in order to

execute that you are saying that hey

this much amount of time you wait now

you obviously can write a function up

here or you can just say hey just go

ahead and use a salary and just wait for

300 times here now this salary obviously

you know that please don't execute it

because that's a bad one you are now

passing up the return value into the set

timeout which obviously you know from

the last video of the closure that we

discussed but you should be passing a

reference that wait for some time and

then do this so this is all higher order

function when you treat your functions

as just like variables it can be passed

on it can be returned as that is a

higher order function I understand this

is a little bit uh too much to digest

for people who are coming up from Lang

languages like C C plus plus we have

never treated functions like this in the

past so this is good now once you

actually explain this all about as a set

timeout which is always a good

indication that how well you understand

so you are taking examples not from high

end but from the very basic which is set

timeout then try to jump into something

like uh let's just say uh we are going

to create a variable uh let's just call

this one as my salaries

whatever they are and this is a variable

not available in arrays so let's just

get values 50 and 40 and 60 and 20 and

then we have 300 400 so don't take too

much long values but these are the

values that we have

now these values right now they are

numbers but they could be values that

are coming up from the database and

obviously you want to process these

values so for example uh maybe you want

to say that hey my salaries I want to

filter the values which are above 50. so

I'm going to just use a filter value and

now there is no way to tell this filter

function that what I want I have to

provide a function which executes

something and give me a result so this

also can obviously be considered as

higher order function and here you can

just simply go ahead and write a

mechanism that hey this is how it's

going to do this so filter actually

takes and loop through all the values

when let's just call each value as n you

can use your regular functions or you

can use these Arrow functions as well

and I'm going to say that n is greater

than 50. so only those values will be

returned to me now obviously I'm not

going to go ahead and do a console log

here because that is too basic here is

the interview series you know what the

result is going to be but why one should

do this why there is a filter that needs

to be used we can go through and do this

with the regular methods like loops and

all these things yes you can do it but

the advantage that you get with the

filter is that you are only focusing on

the Logics and these Logics can be

changed one good example is you can just

keep on chaining these filters can keep

on writing the Logics and then finally

Loop throughout and do the things this

is one of the example that will impress

that using the higher order functions we

are writing very less amount of code

and this code is easy readable

maintainable and going up nicely for

example here in the salaries you want to

do some functions so just pass on the

reference for example you will just pass

on a reference of salary here and here

you will pass on something like a text

so you are calculating the text values

and then you Loop through and do the

things so how easy and readable the code

becomes now because we are using higher

order function that is one of the

advantage here now once you are done

explaining these things like filters and

reduce don't stop there try to explain

that that the first time it clicked to

me and the first time I use it try to

give an example which you have used in

the project and obviously if you have

worked on any project you'll use it like

while the project we did in our first

batch was we wanted to write an async

Handler so the thing handler was

something like this that hey this is a

const and a sync Handler so that we want

to do now why we wanted to build in a

sync Handler the obvious use case in

front of us is we were are interacting

so much with the database and whenever

you interact with the database you have

to use a sync or you probably want to

use a try catch or probably both and

writing those try catch thing again and

again and again will just make our code

files lengthy just like here you can do

all these Logics via Loops but Loops

will take their own space and inside the

loop all you're going to write is the

logic itself so that's why it saves time

this async Handler one utility being

designed outside of the controllers

saved us a lot of line of code so I said

how can we write this a thing Handler so

I just say that hey how do we write the

regular function first let's go through

with that and step by step understand it

so first is this is how you write your

error function great nice there is no

problem in it at all now how can I

convert this so that it accepts function

as a parameter I can go ahead and say

hey accept FN or Fung whatever you like

to call this and this is how it goes

nice and easy the step two is pretty

easy now can I go ahead and pass on this

into a second function so can I do this

so for example I can go ahead and say

hey this is my function and now this

function will do something like this so

for example I go ahead and say hey this

is a narrow function but further is

being processed by somebody and there we

go

now this is only possible because of the

first example in the line 9 this is the

use case we are considered this function

and whatever the output of this you are

just sending it to another one and

understanding this line will actually

take some time but once you click it

that's exactly where you can answer what

is a higher order function now further

down the line what you can do is you can

just go ahead and come up and say hey I

want to make an a sync function just

like this so I'll just use in a sync so

notice how you were able to take a

function and step by step you are able

to treat that function as just a

variable and then after that you just

passed on whatever the result is into

this second function this is exactly

like line number nine we are trying to

do that and now then we are going to go

ahead and simply uh going ahead and

writing in a sync function let me just

go ahead and write this a sync

controller function here so that you

understand what all this actually boils

down and will give you a little bit more

advantage of higher order function and

how it works actually so in this one we

are taking a function as whoever calls

the sync Handler and then we want to use

in a sync so just like in the line

number 15 we are saying so a sync and

what we did in that is request response

and probably go through with the next

this is a little bit of a code from

Express and writing middlewares of it

but don't you worry on that now once we

have this what the whole thing I wanted

to do is wrap everything around the try

catch so in this I simply go ahead and

say hey await and whatever the function

you are passing me

I'm going to go ahead and say request a

response and next

so notice the beauty of this code what

we have in front of us is that anybody

who calls using Handler can just be

absolutely very free can pass me on

function I'll convert that function into

a sync and of eight not only that I'll

wrap it up with a tricad so that makes

my database called really really uh

error free or I'm just handling the

cases here here I can write my catch

cases and here I can just go with that

now if you are able to explain this much

this gives one of the use case that you

have actually used the higher order

function there you are not just

repeating the information which is

available in the mdn and this will

eventually convert into a simple uh kind

of a discussion that hey this guy

actually not only understand the higher

order function this guy understands

what's the implementation are this guy

also one have used it actually into some

of the projects so he is a well-versed

programmer so try to focus not only just

be with these basic examples that filter

is a type of a higher order function or

set timeout as one try to narrate it

with a story by story thing and then you

will obviously be able to impress the

interviewer as well as you will

thoroughly explain him what a higher

order function is with a use case that

you have used in the code but in case

you have never built anything good luck

with them in that case so that's my

brief uh two cents in making sure that

you crack your interview let's catch up

in the next video hope you have already

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