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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.
To add one day to date in JS, the setDate function is the best way. You can create the following function on the Date prototype to add days to the date.ExampleDate.prototype.addDays = function(days) { let d = new Date(this.valueOf()); d.setDate(d.getDate() + days); return d; } let date = new Date(); console.log(date.addDays(1));This will log the next day.
We can set the value of a select box using Javascript using the following. Suppose we have the following select box − Select Apple Strawberry Cherry Guava To set the value of this select element, we need to access it using querySelector. Then set the value. For example −Example// Search the select box const mySelectBox = document.querySelector('#my-select'); // Set the value to 3 or Strawberry mySelectBox.value = 3;
Object-oriented programming languages allow data hiding using private fields. They use these to hide the internals of classes. In JS there is no such in build support to hide/encapsulate the inner workings.We have Anonymous functions that can give you encapsulation in JS. Let us look at an example −Exampleconst HIDDEN_CONST = 100; function fnWeWantToHide(x, y) { return (x + y) * HIDDEN_CONST } console.log(fnWeWantToHide(1, 2))If we write the above code out in the open this code will pollute the global namespace with these names. Instead what we can do is wrap this in an IIFE(immediately invoked functional expressions). For ... Read More
Ajax is a set of web development techniques using many web technologies on the client-side to create asynchronous web applications. With Ajax, web applications can send and retrieve data from a server asynchronously without interfering with the display and behavior of the existing page.Any other technology Ajax also has its own pros and cons. Let's look at some of those.Pros −Allows applications to render without data and fill data as the application gets it from the server.Gives platform independence to application developersFaster page rendersMore responsive applicationsNo rerenders of whole pages are needed to update only a single area.Cons−Any user whose ... Read More