In a language implementing classical inheritance like Java, C# or C++ you start by creating a class–a blueprint for your objects–and then you can create new objects from that class or you can extend the class, defining a new class that augments the original class. In JavaScript you first create an object (there is no … Read more
TLDR JavaScript has lexical (also called static) scoping and closures. This means you can tell the scope of an identifier by looking at the source code. The four scopes are: Global – visible by everything Function – visible within a function (and its sub-functions and blocks) Block – visible within a block (and its sub-blocks) … Read more
You did a great job of summarizing what’s awesome about Node.js. My feeling is that Node.js is especially suited for applications where you’d like to maintain a persistent connection from the browser back to the server. Using a technique known as “long-polling”, you can write an application that sends updates to the user in real … Read more
Ways to clear an existing array A: Method 1 (this was my original answer to the question) A = []; This code will set the variable A to a new empty array. This is perfect if you don’t have references to the original array A anywhere else because this actually creates a brand new (empty) … Read more
The most likely reason for use of single vs. double in different libraries is programmer preference and/or API consistency. Other than being consistent, use whichever best suits the string. Using the other type of quote as a literal: alert(‘Say “Hello”‘); alert(“Say ‘Hello'”); This can get complicated: alert(“It’s \”game\” time.”); alert(‘It\’s “game” time.’); Another option, new … Read more
Given a select element that looks like this: <select id=”ddlViewBy”> <option value=”1″>test1</option> <option value=”2″ selected=”selected”>test2</option> <option value=”3″>test3</option> </select> Running this code: var e = document.getElementById(“ddlViewBy”); var value = e.value; var text = e.options[e.selectedIndex].text; Results in: value == 2 text == “test2” Interactive example: var e = document.getElementById(“ddlViewBy”); function onChange() { var value = e.value; var … Read more
You want the typeof operator. Specifically: if (typeof variable !== ‘undefined’) { // the variable is defined }
Iterating over properties requires this additional hasOwnProperty check: for (var prop in obj) { if (Object.prototype.hasOwnProperty.call(obj, prop)) { // do stuff } } It’s necessary because an object’s prototype contains additional properties for the object which are technically part of the object. These additional properties are inherited from the base object class, but are still … Read more
Current JavaScript From ES6 on you could use template strings: let soMany = 10; console.log(`This is ${soMany} times easier!`); // “This is 10 times easier! See Kim’s answer below for details. Older answer Try sprintf() for JavaScript. If you really want to do a simple format method on your own, don’t do the replacements successively … Read more
Intl.NumberFormat JavaScript has a number formatter (part of the Internationalization API). // Create our number formatter. var formatter = new Intl.NumberFormat(‘en-US’, { style: ‘currency’, currency: ‘USD’, // These options are needed to round to whole numbers if that’s what you want. //minimumFractionDigits: 0, // (this suffices for whole numbers, but will print 2500.10 as $2,500.1) … Read more