JavaScript Code Critique #2


Continuing the process of looking back at some old code that I wrote years ago. This is my 2nd JavaScript code critique. The first one is here.

My goal is to bring hash0 code up to ES5 standards and stop coding like it’s 1990s. Once that’s done, then go on to bring it up to ES6.

Array.prototype.forEach()

Looking through my old code, it looks like I wasn’t taking advantage of the forEach function. I have code that looks like this:

for (var i = 0; i < vm.mappings.length; i++) {
    vm.mappings[i].label = vm.mappings[i].from + ' > ' + vm.mappings[i].to;
}

This works fine, but can be improved with forEach(). For one, the var i is not just in the for-loop’s scope. It also looks messy with a bunch of array accesses with index here and there.

With forEach():

vm.mappings.forEach(function(mapping) {
    mapping.label = mapping.from + ' > ' + mapping.to;
});

Nice.

camelCase

When I first started writing JavaScript, I had just came from the world of C/C++ and PHP, so I was kind of more used to variable_name than variableName. Camel case is the norm so I’ll do that instead from now on.

So from this:

Metadata.prototype.findConfig = function(param, partial_match) {

To this:

Metadata.prototype.findConfig = function(param, partialMatch) {

var hoisting

It’s recommended to declare variables at the top of their scope to make things clear.

I had code where variable declaration is done inside an if-statement.

Metadata.prototype.addMapping = function(from, to) {
    var mapping = this.findMapping(from);
    if (mapping === null) {
        var newMapping = {
            'from': from,
            'to': to
        };
        this.mappings.push(newMapping);
    }
    //...
};

However, the semantic is actually different, so might as well change it to what it is:

Metadata.prototype.addMapping = function(from, to) {
    var mapping = this.findMapping(from);
    var newMapping;
    if (mapping === null) {
        newMapping = {
            'from': from,
            'to': to
        };
        this.mappings.push(newMapping);
    }
    //...
};

Although in this case, I could do without the extra variable too.

Closure

I’ll deviate from hash0 for a bit, and critique code I wrote 3 years ago for AvidTap. I had function declaration within a for-loop, which caused problems. Thankfully nowadays with linters and fully understanding, it’s not an issue anymore.

Imagine something like this:

for (var i = 0; i < notifications.length; i++) {
    var notification = notifications[i];

    var handleTap = function() {
        app.showStore(notification.business_id);
    };

    app.onTap(
        '#notification_' + notification.business_id + '_' + i,
        handleTap;
    );
}

What is clear now wasn’t so clear when I first started. Here the for-loop and the notification variable are in the same exact scope. Each handleTap() function given to app.onTap() will keep a reference to this scope. However, as the for-loop keeps on going, it will keep modifying what notification points to. Remember var hoisting. The result is unexpected behaviour when you actually go to trigger the tap event, because at the time of the tap event the notification variable in the scope would have been changed to reference the last one in notifications array.


That’s all I have time for code critique #2 for now, but it’s great to get it out of my system.