Understand JavaScript’s “this” With Clarity, and Master It

»july. 5 2013 172

(Also learn all the scenarios when this is most misunderstood.)

Prerequisite: A bit of JavaScript.
Duration: about 40 minutes.

The this keyword in JavaScript confuses new and seasoned JavaScript developers alike. This article aims to elucidate this in its entirety. By the time we make it through this article, this will be one part of JavaScript we never have to worry about again. We will understand how to use this correctly in every scenario, including the ticklish situations where it usually proves most elusive.

Bov Academy

of Programming and Innovation

Become an Elite/Highly Paid Specialized Software Engineer (Frontend, Fullstack, etc.)

Within 8–10 Months, Earn MORE than the Avg. New CS Graduate Earns.

45%-Off Tuition for the December Session

By the founder of JavaScriptIsSexy

We use this similar to the way we use pronouns in natural languages like English and French. We write, “John is running fast because he is trying to catch the train.”

Note the use of the pronoun “he.” We could have written this: “John is running fast because John is trying to catch the train.” We don’t reuse “John” in this manner, for if we do, our family, friends, and colleagues would abandon us. Yes, they would. Well, maybe not your family, but those of us with fair-weather friends and colleagues. In a similar graceful manner, in JavaScript, we use the this keyword as a shortcut, a referent; it refers to an object; that is, the subject in context, or the subject of the executing code. Consider this example:

    var person = {
    firstName: "Penelope",
    lastName: "Barrymore",
    fullName: function () {
        ​// Notice we use "this" just as we used "he" in the example sentence earlier?:
        console.log(this.firstName + " " + this.lastName);
    ​// We could have also written this:​
        console.log(person.firstName + " " + person.lastName);
    }
}

  • Receive Updates


If we use person.firstName and person.lastName, as in the last example, our code becomes ambiguous. Consider that there could be another global variable (that we might or might not be aware of) with the name “person.” Then, references to person.firstName could attempt to access the firstName property from the person global variable, and this could lead to difficult-to-debug errors. So we use the “this” keyword not only for aesthetics (i.e., as a referent), but also for precision; its use actually makes our code more unambiguous, just as the pronoun “he” made our sentence more clear. It tells us that we are referring to the specific John at the beginning of the sentence.

Just like the pronoun “he” is used to refer to the antecedent (antecedent is the noun that a pronoun refers to), the this keyword is similarly used to refer to an object that the function (where this is used) is bound to. The this keyword not only refers to the object but it also contains the value of the object. Just like the pronoun, this can be thought of as a shortcut (or a reasonably unambiguous substitute) to refer back to the object in context (the “antecedent object”). We will learn more about context later.

JavaScript’s this Keyword Basics

First, know that all functions in JavaScript have properties, just as objects have properties. And when a function executes, it gets the this property—a variable with the value of the object that invokes the function where this is used.

The this reference ALWAYS refers to (and holds the value of) an object—a singular object—and it is usually used inside a function or a method, although it can be used outside a function in the global scope. Note that when we use strict mode, this holds the value of undefined in global functions and in anonymous functions that are not bound to any object.
Continue Reading

12 Simple (Yet Powerful) JavaScript Tips

»feb. 20 2013 38

(For Badass JavaScript Development)

NOTICE: I have written only 2 of the 12 tips so far, but I plan to post all 12 Powerful Tips eventually.

I provide you with 12 simple, yet powerful, JavaScript tips and detailed explanation of each. These are techniques that all JavaScript programmers can use now; you needn’t be an advanced JavaScript developer to benefit from these tips. After you read all of the detailed explanations of how each technique works and when to use it, you will have become a more enlightened JavaScript developer, if you aren’t already one.

Indeed, notable JavaScript masters and enlightened JavaScript developers have been using many of these techniques to write powerful, efficient JavaScript. And in a bit, you will, too.

Bov Academy

of Programming and Innovation

Become an Elite/Highly Paid Specialized Software Engineer (Frontend, Fullstack, etc.)

Within 8–10 Months, Earn MORE than the Avg. New CS Graduate Earns.

45%-Off Tuition for the December Session

By the founder of JavaScriptIsSexy

  1. Powerful JavaScript Idiomatic Expressions With && and ||

    You see these idiomatic expressions in JavaScript frameworks and libraries. Let’s start off with a couple of basic examples:

    • Receive Updates


    Example 1: Basic “short circuting” with || (Logical OR)
    To set default values, instead of this: Continue Reading