The 10 Most Common JavaScript Issues Developers Face

# The 10 Most Common JavaScript Issues Developers Face At first, JavaScript may seem quite simple. Yet the language is significantly more nuanced, powerful, and complex than one would initially be led to believe. Many of JavaScript’s subtleties lead to a number of common problems—10 of which we discuss here—that keep code from behaving as intended. It’s important to be aware of and avoid these pitfalls in one’s quest to become a master JavaScript developer. ... **In fact, many of JavaScript’s subtleties can lead to a number of common problems that keep it from working—10 of which we discuss here. It is important to be aware of and avoid these issues on your journey to become a master JavaScript developer.** ## JavaScript Issue No. 1: Incorrect References to `this` There’s no shortage of confusion among JavaScript developers regarding JavaScript’s `this` keyword. As JavaScript coding techniques and design patterns have become increasingly sophisticated over the years, there’s been a corresponding increase in the proliferation of self-referencing scopes within callbacks and closures, which are a fairly common source of “ … ## JavaScript Issue No. 2: Thinking There Is Block-level Scope As discussed in our JavaScript Hiring Guide, a common source of confusion among JavaScript developers (and therefore a common source of bugs) is assuming that JavaScript creates a new scope for each code block. Although this is true in many other languages, it is … ## JavaScript Issue No. 3: Creating Memory Leaks Memory leaks are almost inevitable issues in JavaScript if you’re not consciously coding to avoid them. There are numerous ways for them to occur, so we’ll just highlight two of their more common occurrences. … ## JavaScript Issue No. 4: Confusion About Equality One JavaScript convenience is that it will automatically coerce any value being referenced in a boolean context to a boolean value. But there are cases in which this can be as confusing as it is convenient. The following expressions, for example, are known to be troublesome for many a JavaScript developer: … ## JavaScript Issue No. 5: Inefficient DOM Manipulation JavaScript makes it relatively easy to manipulate the DOM (i.e., add, modify, and remove elements), but does nothing to promote doing so efficiently. A common example is code that adds a series of DOM elements one at a time. Adding a DOM element is an expensive operation, and code that adds multiple DOM elements consecutively is inefficient and likely not to work well. … ## JavaScript Issue No. 6: Incorrect Use of Function Definitions Inside `for` Loops Consider this code: ``` var elements = document.getElementsByTagName('input'); var n = elements.length; // Assume we have 10 elements for this example for (var i = 0; i < n; i++) { elements[i].onclick = function() { console.log("This is element #" + i); }; ``` … ## JavaScript Issue No. 7: Failure to Properly Leverage Prototypal Inheritance A surprisingly high number of JavaScript developers fail to fully understand, and therefore fully leverage, the features of prototypal inheritance. Here’s a simple example: ``` BaseObject = function(name) { if (typeof name !== "undefined") { this.name = name; } else { this.name = 'default' }; ``` … ## Understanding the basics ### What are the common errors in JavaScript? The common errors that developers make while coding in JavaScript include mistaken thinking about how the “this” keyword works, incorrect assumptions about block scoping, and a failure to avoid memory leaks. JavaScript’s evolution over time has left many pitfalls if old coding patterns are followed.