To get a subset of object's properties and create a new object out of those properties, use object destructuring and property shorthand. For example, You have the following object −Exampleconst person = {    name: 'John',    age: 40,    city: 'LA',    school: 'High School' }And you only want ... Read More

Nothing. They can get to V8 speed if proper investments are made in optimizing those language engines as are made for JS by Google in the V8 project.This is all really a matter of how much push is provided to the language by sponsoring organizations to further the development and ... Read More

The parseInt function available in JavaScript has the following signature −SyntaxparseInt(string, radix);Where the parameters are the following −string − The value to parse. If this argument is not a string, then it is converted to one using the ToString method. Leading whitespace in this argument is ignored.radix − An integer ... Read More

Arrays can be compared in 2 ways −They refer to the same array object in memory.They may refer to different objects but their contents are all equal.ExampleFor case 1, jasmine provides the toBe method. This checks for reference. For example, describe("Array Equality", () => {    it("should check for array ... Read More

In modern browsers, if a DOM Element is removed, its listeners are also removed from memory in javascript.Note that this will happen ONLY if the element is reference-free. Or in other words, it doesn't have any reference and can be garbage collected. Only then its event listeners will be removed ... Read More

The difference between 'throw new Error' and 'throw someObject' in javascript is that throw new Error wraps the error passed to it in the following format −{    name: 'Error',    message: 'Whatever you pass in the constructor' }The throw someObject will throw the object as is and will not ... Read More

Future is an old term that is same as promise.A promise represents a value that is not yet known. This can better be understood as a proxy for a value not necessarily known when the promise is created.A deferred represents work that is not yet finished. A deferred (which generally ... Read More

There is no solid reason to choose jasmine over jest. Both are excellent libraries that have been around for a while and have an opinionated way of doing things that are quite similar. Jest is built on top of jasmine.One reason why you might choose jasmine over jest is that ... Read More

SinonJS provides stand-alone test spies, stubs and mocks. It is a library that we can use to create object mocks for unit testing.Spies − Fake functions that we can use to track executions.Stubs −Functions replacements from which we can return whatever we want or have our functions work in a ... Read More

JS has 2 notations for creating object properties, the dot notation and bracket notation.To create an object property from a variable, you need to use the bracket notation in the following way −Exampleconst obj = {a: 'foo'} const prop = 'bar' // Set the property bar using the variable name ... Read More