Some interview question for frontend developer

What is javascript?

Javascript is a scripting and programming language to allow implement complex features on page. Javascript make a web page very attratctive and dynamic. Javascript have many framework and library to make web application colorful and dynamic.

What is the difference between Double equal(==) and Triple (===)?

Double equal and triple equal mainly same thing. But they have a big difference. Double equal check just value. Double equal find out many types of value. But triple equal is very strict. Triple equal check value and exact type.

What is the difference between Null and undefined?

Undefined is a mistake that programmer do unfortunately. Basically when we forget to define a value. that the javascript give us undefined result. Null is a common thinks that programmer use intentionally for their purposes.

How to work javascript event loop?

Javascript is a non-blocking programming language. It work serial wise. Javascript work one by one in his serial. This sequence call javascript event loop.

Asynchronous Javascript setTimeout, setInterval

Javascript work one by one. Sometimes we need set time in function. That this time javascript don’t wait for this time. After finished this time then implement this function

How to event bubble work?

Event bubble is very tricky things. If I clicked a li item. They at this we also clicked ul item and container item. Because ul and container is parent item of li. That’s why we call, when I clicked a item. That this we also clicked this item’s parent item.

What is DOM?

DOM is document object model. Javascript cannot understand html elements. Javascript understand object. That’s html converted document. So, DOM is document object model which is javascript object.

What is an API?

API is server container where we got data. And send data. API usually make by node.js. Node help us maintain server side. Sometime we need data then we got data from api. and we also send data. and we can update api data.

The purpose of API, GET, POST?

Sometimes we need ready data. And this data make by me or other data. This sequence call api. We got data from api by get method. We need to send data into api. We send data in api by using post method.

What is arrow function?

Arrow function is implement with es6. Arrow function declaration system like a variable declaration. Arrow function help programmer to set a function. Basically javascript last updated was in 2015. That’s time arrow function add in javascript language.