ES6 Interview Questions and Answers
Most Frequently Asked ES6 Interview Questions
|ES5 is the 5th edition of ECMAScript which was standardized in 2009. This version has been successfully implemented in all web browsers.||ES6 is the 6th edition of ECMAScript which was standardized in 2015. This version has been partially implemented in most web browsers.|
|The function keyword is mandatory to use to define the functions.||In this, to define the function, the function keyword is not needed.|
|The return keyword is also mandatory to use to define the functions||The return keyword is not needed to define the functions.|
|ES5 has lower performance due to the absence of a few features.||ES6 has a comparatively higher performance.|
IIFEs or Immediately Invoked Function Expressions are the expressions which are immediately executed as soon as it is created. IIFEs are used to avoid the excessive use of global namespace because all the variables which are used inside the IIFE cannot be viewed outside its scope. In other words, IIFEs are design patterns also known as Self Executing Anonymous Functions because it executes on its own.
Arrow functions are one of the major reasons for the popularity of ES6 due to the reasons mentioned below:
- Safety of scope: Consistent use of arrow functions guarantee to use the same thisObject as the root. Using the arrow functions provides scope safety because even if a single standard function callback is mixed with some arrow functions, the probability of scope getting disturb increases.
- Compactness: It is easier to read and write when it comes to arrow functions as compared to other functions. This provides a less complex approach of using ES6 as well as the arrow functions.
- Provides clarity: A developer can easily identify what “ thisObject” is and find out the next-higher function statement after the arrow function statement if he/she uses arrow function in most of the program. It will provide huge clarity and easy detection of errors in any program.
As far as coding in a functional paradigm is concerned, using the spread syntax in ES6 can prove to be heavily beneficial. The spread syntax can be easily used to create copies of arrays or objects. Using spread syntax in a program does not need to resort to Object.create, slice or any library function. The spread syntax is widely used in Redux and rx.js projects.
Note: This question is asked in almost all ES6 Interview Questions.
|ES6 class||ES5 Function Constructors|
|ES6 class basically does the work of defining a new object and appending functions to its prototype.||ES5 Function constructors work and look the same but the main difference is observed when the developer uses the Inheritance property.|
|They can be considered as the syntax base for constructor functions.||These can only be executed with the help of a new operator.|
|ES6 class allows the developers to instantiate objects using the new operator.||ES5 function constructors focus on how the objects are instantiated.|
|They also ensure the developer that this keyword which is basically used inside the class only refers to the object that is being created by the developer.||ES5 function constructor focus on implementing the reusable object creation code. Any function can be used as a constructor.|
|.call is used to invoke the functions, and the first parameter will become the value of this within the function created by the developer.||.apply is also used to invoke the functions but it takes an array of arguments. This array works as the next argument and the function works this way.|
|.call is used to call the method which takes the owner object as its argument.||.apply method is used to write methods. These methods can be used on several objects.|
|It accepts two parameters namely objectInstance and arguments||It accepts two parameters namely objectInstance and arrayofArguments|
|.call takes several arguments separated by commas.||.apply takes several arguments with the help of an array of arguments.|
ES6 classes have been found to be very useful to the developers. Some of the major uses of ES6 classes are as follows:
- ES6 classes have a simpler and less error-prone syntax.
- As far as setting up inheritance hierarchies are concerned, ES6 is considered as the best option as it uses new syntax with the old syntax which minimizes the errors and eases the process.
- ES6 classes help in defending the developers from failing to use new ones properly with the constructor function. This is one of the most common errors that occur with the developers during the use of a new operator. Classes remove this error by having the constructor throw an exception if this proves to be an invalid object for the constructor.
- Classes also help to call the method which is of the prototype’s version. This version is much simpler with the new ES6 syntax than the old versions.
With the launch of ES6, a new way of working with functions and iterators came into work. These are called generators. A generator is nothing but a function that can stop at the point of time when the user commands it to do so and then continue working just from the point where it stopped. In other words, a generator has properties of a function but also works as an iterator. It does not work like other lines of code which need to be completed for execution.
Generators work on a run-to-completion model which makes it easier for the developers to compile a program. Generators can also be defined as a special class of functions that work to simplify the task of coding iterators in a program. It produces a sequence of results rather than producing a single value. It enables the developer to generate a series of values at a time.
Spread Operator- Donated by ‘...’ and is followed by the variable. The syntax of the spread operator would look like this for example:- ‘...X’. Spread operators manipulated objects and arrays which is the prime reason it is used in ES6. It is used for copying the property of one object to another.
Default Operator- In order to initialize a function using default values, the default operator is deployed. The parameter’s value can be anything- a number or a function or null.
Rest Parameter- This operator is used for recovering all the arguments that are required to invoke a function. This allows us to put items belonging to different categories separate. The rest parameter allows combining the parameters in a common array parameter.
Class- You can use the patterns easily with OOP based class declaration. It works readily with constructors, supports base class access, inheritance and static methods. OOP refers to Object-Oriented Programming.
Proxies- With proxies, you get to create objects and you can host the objects with a huge behavior diversity. Proxies can help in profiling and logging as well.
You can call the immutable variables as constants. The value of a constant once defined remains the same and we cannot change it. This is the value that you introduce during the declaration. For example, const Y= 6.0. This value of Y would continue to be 6 throughout and it won’t be changed.