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Perl is a programming language developed by Larry Wall, specially designed for text processing. It stands for Practical Extraction and Report Language. It runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX Following great features make this language necessary for the Programmers to learn −Perl is a stable, cross-platform programming language.Though Perl is not officially an acronym few people used it as Practical Extraction and Report Language.It is used for mission-critical projects in the public and private sectors.Perl is an Open Source software, licensed under its Artistic License, or the GNU General ... 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 it is faster. (https://github.com/facebook/jest/issues/6694)
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 way that suites us to be able to test multiple scenarios.Mocks −Fake methodsAll these objects help in unit testing our code.
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 prop obj[prop] = 'baz' console.log(obj);OutputThis will give the output −{ a: 'foo', bar: 'baz' }ES6 introduces computed property names, which allow you to do −Exampleconst prop = 'bar' const obj = { // Use a as key a: 'foo', // Use the value of prop ... Read More
You can't break from the forEach method and it doesn't provide to escape the loop (other than throwing an exception).You can use other functions like _.find from lodash instead −_.find − it breaks out of the loop when the element is found. For example,Example_.find([1, 2, 3, 4], (element) => { // Check your condition here if (element === 2) { return true; } // Do what you want with the elements here // ... });Throw an exception from forEach. For example,Exampletry { [1, 2, 3, 4].forEach((element) => { // Check your condition here if (element === 2) { throw new Error(); } // Do what you want with the elements here // ... }) } catch (e) { // Do nothing. }
The most efficient method to group by a key on an array of objects in js is to use the reduce function.The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in a single output value.Exampleconst people = [ { name: 'Lee', age: 21 }, { name: 'Ajay', age: 20 }, { name: 'Jane', age: 20 } ]; function groupBy(objectArray, property) { return objectArray.reduce((acc, obj) => { const key = obj[property]; if (!acc[key]) { acc[key] = []; ... Read More
You can dispatch events on individual elements using the dispatchEvent method. Let's say you have an element test with an onChange event −Event handler −document.querySelector('#test').addEventListener('change', () => console.log("Changed!"))Triggering the event manually −const e = new Event("change"); const element = document.querySelector('#test') element.dispatchEvent(e);This will log the following −Changed!
To clear a localStorage data on browser close, you can use the window.onunload event to check for tab close.Let's say you have a local storage object called MyStorage as a global for the sake of this example. Then you can write an event handler −Examplewindow.onunload = () => { // Clear the local storage window.MyStorage.clear() }This will clear the local storage on the tab/window close.
MEAN is an acronym for MongoDB, Express, Angular, and Node.js.MEAN.js and MEAN.io are the same things essentially as they both are scaffolded applications or a basic set up to use the above 4 things. These libraries/tools have these set up for you already.These allow you to not spend time on setting up the basic infra, rather focus on building the application.
We can use the Node.contains method to do this check. The Node.contains() method returns a Boolean value indicating whether a node is a descendant of a given node, i.e. the node itself, one of its direct children (childNodes), one of the children's direct children, and so on.ExampleFor example, you are looking for an element with id test, you can use the following −const elem = document.querySelector('#test'); console.log(document.body.contains(elem));This will log true or false based on whether the element is present in the visible DOM.