Top 30+ Underscore.JS Interview Questions

If you are to do any interview relating to the Undwerscore.js framework, you need to anticipate whatever the interviewing panel is likely to ask. In such a case, we deem it fit to provide you with such common 30 Underscore.JS interview questions and answers that can help you convince the interviewing panel that you are ideal for the Underscore.JS tasks.

1. What is Underscore.JS?

It’s a JavaScript library with functional programming helpers that do not require an extension of built-in objects. Underscore.JS users can enjoy more than 100 functional helpers capable of supporting map, invoke, filters, and other functional helpers. It also provides specialized functions such as function binding, creating quick indexes, JavaScript templating, and deep quality testing. 

2. What are collection functions in Underscore.JS  framework?

These functions operate on objects, arrays, and array-like objects like NodeList, arguments, and similar. The common collection functions used in Underscore.JS includes

  • each
  • map
  • find
  • filter
  • reject

3. What is the importance of the Underscore.JS -max function?

The _.max() function in Underscore.JS finds minimum elements from the passed list. Incases an iterate is provided, it’s applied to every value and generates criteria for value ranking and finding minimum elements. 

4. Explain the features of Underscore.JS 

  • Collections: These functions allow develoepsr5 to apply operations on every item within a collection. Using methods like min, max, countBy, and groupBy found in the collection feature will make work easier when handling many tasks. Under collection, you’ll also find reduce, map, and each. 
  • Objects: Various functions in Underscore are used for object manipulation, mapping of objects, and comparison of objects. These functions include extends, isEqual, value, keys and isEmpty
  • Arrays: there are various functions in Underscore.JS that helps with the iteration and processing of arrays. These functions include intersection, difference, lastIndexOf, initial, and first. 
  • Utilities: there are several utility methods in Underscore.JS like random, escape, noConflict, and iterate
  • Functions: delay, bind, after, and before are among the essential functions provided by Underscore.JS. 
  • Chaining: there are also chaining methods in Underscore.JS like value and chain

5. What are browser engines compatible with underscore js?

All engines that support Es3 are compatible with underscore js. Furthermore, it also utilizes new features such as typed arrays, object.key, and ES modules. We have listed a list of the engines that fully support the Underscore js framework below

  • Edge 13, 18, and the latest
  • Internet Explorer 9–11
  • Safari 8–the latest
  • Chrome 26–the latest
  • Firefox 11–the latest
  • Node.js 8–latest LTS
  • Adobe ExtendScript

6. Differentiate between allKerys and keys object functions

We use the object function keys _.keys(object) to retrieve the name of enumerable properties of an object. On the other hand, allKeys _.allKeys(object)retrieve the properties inherited by the object and its properties. 

7. What is mapObject in Underscore.JS?

mapObject is an object function that works like a map, but instead, it does the transformation of each object property in turn. 

8.      What is the role of _.constant(value) in Underscore.JS?

It’s a utility function that returns a similar value used in our argument

9.      What is mixin?

This utility function allows developers to extend the Underscore.JS library with their own utility functions. By passing {name: function} definitions, your function will be added to the underscore object and OOP wrapper. Mixin will also return the underscore.js object for the facilitation of chaining. 

10. Explain what template in Underscore.JS is

Using the code line _.template(templateString, [settings]), one can compile JavaScript templates to functions. These functions can later be evaluated for rendering. In short, a template can execute arbitrary JavaScript codes and interpolating values.

11. Explain how we can use find and findwhere collection functions

Find is a collection function that searches for every value in the list and then returns the value that will pass the truth test first. If no value passes the test, the find function returns undefined. Once it finds accepted value, it will return instantly. On the other hand, findwhere will scavenge the list for key-value pairs in the properties and return the first value if it’s true. Suppose the list is empty, or no value is found; it returns undefined. 

12. When do we use flatten Array Function?

When developing an application using underscore JavaScript, you can use the _.flatten(array, [depth]) command to flatten nested arrays. A single level flattens the array if it passes a depth of 1 or a true value. However, you’ll descend deeper in your nesting hierarchy when you pass greater value.

13. What does _.union(*arrays) do?

It’s a function in Underscore.JS used for computing the union of passed-in arrays, a list of similar items in a given order available in one or more arrays. 

14. When do we use the zip collection array?

We use the zip function when we want to marge values of arrays at a corresponding position. It’s practical to use separate data sources coordinated via matching array indexes. We use the*arrays) code line in such a case. 

15. What are the advantages of using Underscopre.js?

  • It’s an open-source code 
  • have massive community support
  • Support many browser engines
  • Rich library with extensive functions
  • Easy to learn and implement
  • Compatible with other frameworks

16. What are the drawbacks of the underscore JavaScript framework?

  • Underscore.JS rely on JavaScript knowledge, and without it, it may take young developers to archive a reasonable project.
  • It requires code lines to be able to perform simple tasks.

17. Explain scenarios when we use Reduce and reduceRight

Reduce is also referred to as fold or inject. It is used when you want to reduce a list of values into distinct values. We use memo to begin the reduction process; we use iteratee to return the value. In iterate, we pass the memo, value, index, and finally, the list using the command _.reduce(list, iteratee, [memo], [context])

Reduceright, also known as foldr, is useful in a programming language with lazy evaluation. But its function isn’t much exploited in the java language.

18. What is reject in Underscore.JS?

Using _.reject(list, predicate, [context]), we can return values that aren’t in the list that pass the truth test

19. Throttle is an array function in Underscore.JS; what does it do?

We use this function when we want the compiler to return a new and throttled version of passed functions. When these functions are invoked repeatedly, they’ll call our original function once per millisecond. When we want to rate-limiting events with faster occurrence, we use the throttle function. 

20. What is debounce?

Its underscore function is used for creating and returning debounced versions of the passed function, postponing its execution until a millisecond elapses since the last invoking. 

21. Name the commonly used Object Functions in Underscore.JS 

The common object functions found in the underscore JavaScript framework include Keys, allKeys, values, mapObject, pairs, Defaults, clone, tap, toPath, get, has, property, propertyOf, matcher, isEqual, isMatch, isEmpty, isElement, isArray, isObject, invert, create, functions, findKey, extend, extendOwn, pick, omit, etc.

22. What are the Underscore.JS Utility Functions?

Underscore has various utility functions that can be used to perform various tasks. Some of these function utilities are noConflict, identity, constant, noop, times, random, mixin, iterate, uniqueId, escape, unescaped, result, now, and template

23. When do we use _.chain(obj)?

When we want to return values of wrapped objects in Underscore.JS, by continuously calling methods on chain object, it will continuously return wrapped objects until the process recall the value. 

24. What is Underscore. String?

It’s an extension that adds a function for string manipulation

25. How can you install JS on your system using node.js?

To install undercore.js on your system, ensure you have installed npn and node.js on the target system. After that, use the command npm install underscore to install the Underscore.JS framework. 

26. Explain how you can install underscore using the Underscore.JS file

To install undercore.js fram3wiork using this method, one has to download the Underscore.JS file from the official store. Once on the site, confirm that you’ve got the download button to be able to download the last version. Select save as, and once the download is complete, add underscore-min.js in the script tag, and you can start programming using the Underscore.JS framework.

27. Why should you consider Modular Import in Underscore.JS?

We can consider using modular import if you want to create a customized build of underscore.JS

28. When can I sue .contains(list, value, [fromIndex])?

Contains is Collection Function that returns a true if the argument value is found in the list of arrays. We use a list if we are working on an array, fromIndex enables us to start our search from a given index. 

29. What is shuffle?

In Underscore, we use shuffle to obtain a shuffled copy of our list. This is done using the Fisher-Yates shuffle version.

30. Who developed Underscore.JS?

Underscore.JS framework was developed by Julian Gonggrijp and Jeremy Ashkenas before. The first release of underscores was on October 28, 2009. Today’s most stable release is 1.13.4, released on June 2, 2022. 


With the information we’ve provided here, it’s easier to respond to all the questions you’ll be asked during Underscore.JS interviews. However, one must also work on the confidence aspect to be able to answer all the questions while looking composed. 

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