Front End Technology Articles - Page 474 of 860

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.

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

You can use lodash's set method to set properties at any level safely. Setting first-level properties are pretty straightforward. Nested property access is tricky and you should use a tested library like lodash for it.You can set a deeply nested object in the following way −Examplelet _ = require("lodash"); let obj = {    a: {       b: {          foo: "test"       },       c: 2    } }; _.set(obj, "a.b.foo", "test1"); _.set(obj, "a.c", { test2: "bar" }); console.log(obj);OutputThis will give the output −{ a: { b: { foo: 'test1' ... Read More

You can use lodash's get method to get properties at any level safely. Getting first-level properties is pretty straightforward. Nested property access is tricky and you should use a tested library like lodash for it.You can access a deeply nested object in the following way −Examplelet _ = require("lodash"); let obj = {    a: {       b: {          foo: "test"       },       c: 2    } }; console.log(_.get(obj, "a.b.foo")); console.log(_.get(obj, "a.c")); console.log(_.get(obj, "a.test")); console.log(_.get(obj, "a.test.x"));OutputThis will give the output −test 2 undefined undefinedYou can also write your own ... Read More

You can use lodash's get method to get properties at any level safely. Getting first-level properties is pretty straightforward. Nested property access is tricky and you should use a tested library like lodash for it.You can access a deeply nested object in the following way −Examplelet _ = require("lodash"); let obj = {    a: {       b: {          foo: "test"       },       c: 2    } }; console.log(_.get(obj, "a.b.foo")); console.log(_.get(obj, "a.c")); console.log(_.get(obj, "a.test")); console.log(_.get(obj, "a.test.x"));OutputThis will give the output −test 2 undefined undefinedYou can also write your own ... Read More

The query string is made up of query parameters and used to send data to the server. This part of the URL is optional. It needs to be constructed by the developer. This can be done using a native method called encodeURIComponent.The encodeURIComponent() function encodes a Uniform Resource Identifier (URI) component by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the characterUsing the new ES6 format, objects can be query string encoded in the following way −Examplelet obj = {    name: 'John',    age: 25,    city: 'Chicago' ... Read More

In JavaScript, objects are the collection of a key value pairs. The properties of the object are the keys and is denoted with a string. The value of the key is the value of the property of the given object. Types/Techniques of object copying There are 2 types of copying objects in any language namely: deep copy, and shallow copy. Shallow Copy In this technique an object is copied as little as possible. For suppose if you copy a collection using this technique the structure of the collection is copied to the destination, not the elements. Example Following is an ... Read More