JavaScript as a First Language


At Khan Academy we’ve been investigating teaching Computer Science to students in some new and interesting ways. The most interesting aspect of which is that we’re likely going to be teaching them JavaScript as their first language.

We’re in a very unique position as we’re primarily aiming to teach students who’ve been through our previous math and science-centric curriculum. Because of this we can create some rather compelling exercises and projects that never would’ve been feasible otherwise.

The prospect of teaching the JavaScript language as a first language is actually really exciting. Teaching prototypal inheritance to experienced classical-inheritance-using developers is normally rather frustrating (and results in many libraries springing up attempting to replicate the classical style of inheritance in JavaScript, which is a whole realm of weirdness in-and-of itself). Teaching prototypal inheritance to someone who has never seen any form of inheritance before will decidedly be an easier task. The same goes for learning functional programming. JavaScript is a great language for experiencing functional programming and can be a major focus of our curriculum as a result.

As we’ve begun to look at the prospect of JavaScript-as-a-first-language a number of obvious warts stick out (as is obvious to anyone who has worked with JavaScript for any duration). To make sure that general warts don’t crop up we will be using some form of linting (either JSLint or JSHint or similar) in the code editor to give the users contextual information on what’s happening with their code and why they should be writing their code in a certain way.

We want to go beyond basic syntax tweaks though and find ways of using the language that’ll result in an easier learning experience. In particular there are two changes which will likely result in a much simpler on-ramp to learning.

Note: These particular recommendations really only make sense if you’re teaching JavaScript to someone who has never seen the language before and is really only programming with a set of specific, well-coded, libraries. Obviously more will have to be taught in order bring the students up to the level of “see any random piece of cross-browser JavaScript code and understand what it does.”

Type Coercion

Type coercion is just a complete mess, as many many others have pointed out and as what Douglas Crockford typically teaches, as in JavaScript: The Good Parts.

It might make sense to discuss it far later in the education cycle… like after learning about prototypes, functional programming, and closures. Basically after everything that’s actually important.

  1. name === "John"

The first change that I’m recommending is that the students will only ever see, and use, === (and !==). While using ‘==‘ does have the advantage of being syntactically shorter there is so much type coercion baggage attached to it as to make it an exercise in futility to try and teach early on in the learning of programming.

The one exception that might be worthwhile to teach later on is the case in which you wish to see if a variable contains a null or undefined value. This can be done easily with a simple someVar == null check and is likely the one useful case of ==. (Another noted exception is the browser bug in IE where === checks against Window objects will always return false, but it’s unlikely that we’ll cover such specific browser issues in our curriculum.)

Falsy Values

For the same reasons that == can be messy, so can falsy values. Enforcing strict boolean checks would result in less edge cases but would certainly result in longer code. Perhaps education of falsy values can be limited to booleans, null, and undefined with number and string falsy values left for a later exercise.

Function Declarations

Perhaps the most interesting change that we can make is a rather subtle one, but it’s eschewing normal function declarations for creating anonymous functions and assigning them to a variable.

  1. // Don't do this:
  2. function getData() { }
  3.  
  4. // Do this instead:
  5. var getData = function() { };

There are a number of good habits that are instilled when you use this particular technique.

  • Makes it easier to understand “functions as an object”. I’ve found that when you show new developers a function being assigned to a variable it suddenly becomes much more obvious that a function is actually an object and can be manipulated as such (and that a function can be passed as an argument to another function). Thus students are advanced along the path towards a better understanding of functional programming.
  • It enforces good semicolon habits. Traditional function declaration is the only situation in which semicolons aren’t needed (save for conditional statements and loops, naturally) and it makes it much more obvious when they’re required all the time.
  • Doesn’t have much of the baggage traditionally associated with functions and scope.

Block Scope

This is the remaining area that’ll certainly be a challenge for any introductory student to understand and yet I don’t see a particularly good solution here. The issue of variables declared within for loops hoisting up is more than enough to make most developers heads spin. I’ll have to see if we can’t come up with some intuitive ways of explaining how variable declaration works (and combining it with vigilant lint enforcement) rather than having a purely technical solution.

(While (function(){ ... })(); is a solution I’m skeptical that we’ll be able to teach that early-enough on as to make it worthwhile.)

JavaScript as a First Language

It should be noted that while we’re starting with JavaScript as a first language – largely due to its ubiquity, desirability in the larger workforce, lack of prior installation requirements, and ability to create something that’s easy to share with friends – we’re not going to be myopic and only focus on JavaScript. There are so many things that can be learned from other languages, not to mention entire skillsets that aren’t terribly relevant to in-browser JavaScript, that it behooves us to try and bring as much of them into our curriculum as possible.

I talk a little bit more about our choice to use JavaScript and some of the browsers that we’ll want to support in our development in the following video:

By all accounts I want to try and avoid any features that would cause cross-browser weirdness to spring up. As a result we’ll be making extensive use of libraries (for drawing to a canvas or manipulating the DOM) and using only JavaScript language features that work consistently in the browsers that we end up supporting.

Posted: December 21st, 2011


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