JavaScript Review Notes

These are items that any code reviewer should keep in mind when reviewing JavaScript.

Contents

JavaScript Review Notes

CRITICAL

ALL JAVASCRIPT FILES MUST BE LINT-FREE
- Note though that you can sometimes confuse XmlLint [1]
NO SCRIPT FILES SHOULD BE PULLED IN BY THE YAHOO CDN (use these instructions to add the scripts properly)
ANY DISPLAY OF TEXT INPUT MUST BE TESTED FOR PROPER ESCAPING. If this isn't tested, we don't know that we're safe against HTML injections.
NEVER DO YUI().use IN LAUNCHPAD TEMPLATES. Always use LPS and do LPS.use in Launchpad templates.
- LPS is an instance of YUI that has been initialized in the base template and passed YUI config parameters. Using LPS ensures we use a YUI object consistently. You should never need a YUI().use block before LPS has been initialized; if you think you do, you must restructure your code.
DON'T PERFORM JS LOGIC IN TEMPLATES Always include a module of JS that is testable and performs the logic. At most, the template file should be running a run() or init() method.

Building

To build the javascript run:

make jsbuild

More info: JavaScript Build System

Plain Old JavaScript

JavaScript blocks should be indented by 4 spaces.
If 3 or more lines of strings are to be joined together, use the [str1, str2, ...].join("") form.
1 and 2 character variable names are to be avoided.
Regular expression literals should be avoided.
All public or protected functions, methods, and object properties should be described with JSDoc comment strings and tags.
- Module-level private variables don't need full JSDoc tags.
C++ style comments ("//") should only be used inside function bodies.
Per-line var statements are preferred inside function bodies.
As vars are hoisted, declare vars at the top of function or global scope.
Function, method, and variable names should follow the PEP 0008 style guide (and no, this is not how the rest of the world does it).
Any string literal used more than once in a file should be assigned to a CONSTANT (a variable, really) so that the minifier can compile it to a short name.
functions should always return null not undefined.
To make conditionals explicit but readable, use the Y.Lang.isXXX methods: Y.Lang.isArray, Y.Lang.isObject, Y.Lang.isValue, and others.

XHTML, CSS, and Styling

CSS files should come before JavaScript files in the document head.
CSS url() directives should have the file name surrounded by single-quotes: url('spinner.png')
XHTML attributes should be surrounded by double-quotes: <input type="text"/>
Setting a node's style explicitly with setStyle() should be avoided.
To set a node's style, it is preferable to add a CSS class to the node, and let the stylesheet handle the presentation. [2]
Please use the W3C markup validation service to check what you write, and to check what the DOM looks like after AJAX inserts new elements.

Event Handling

"e" should be used as the event object variable name in event handlers: function onclick(e) {...}
event.halt() should be preferred over event.stopPropagation(), event.preventDefault(), or e.returnValue = false
Document-wide keypress handlers are dangerous, and should be detached as soon as they are no longer needed.
Key event handling sucks. The best cross-browser reference we've found to date is at http://unixpapa.com/js/key.html and for an example in our code, see lib/lp/registry/templates/product-new.pt.

Javascript Module formatting

Modules should have a JSDoc string with the @module or @submodule tag.
Module-body content does not have to be indented.
Module-wide constants should go at the top of the file, after the module JSDoc string.
Multi-line var statements may be used in the module-wide constants block.
Script tags included for local development should be wrapped in <tal:devmode condition="devmode"></tal:devmode> tags so that un-minified scripts are only loaded for dev usage.

Naming Javascript Modules and Namespaces

The file path, the module name, and the namespace should correspond to each other.
- For example:
  - File path: lib/lp/code/javascript/subscription.js
  - Module name: Y.add( "lp.code.subscription" , ...
  - Namespace: var module = Y.namespace( "lp.code.subscription" );
A module's public functions should be attached to the namespace variable and not be attached directly to the Y.namespace_name variable.
- Do this:
```
var module = Y.namespace("lp.code.subscription");
module.my_public_function = function() {};
var my_private_function = function() {};
```
- Don't do this, since Y.namespace() will create a new Y.lp object and Y.lp.calendar object if they don't already exist.
```
Y.lp.calendar = Y.namespace("lp.code.subscription");
```
- Don't do this, since it will be easier to change the module name and namespace, if you only have to do it in one place in the module.
```
var module = Y.namespace("lp.code.subscription");
Y.lp.calendar.my_public_function = function() {}; // Should use `module` variable here.
```

It will then be possible to use module functions like this:

Y.use("lp.code.subscription", function() {
    Y.lp.code.subscription.my_public_function();
});

Widgets and Plugins

Protected and private method names should be prefixed with an underscore.
All protected methods should have the @protected JSDoc tag, even ones like initializer() and renderUI().
Event handler method names should be prefixed with _on or _after.
Custom events should be documented on the line immediately preceding the line where they are published.
All JSDoc strings for attributes should have @attribute, @type, and @default tags.
Objects such as Node instances should not be instantiated in the widget's ATTRS hash using value:, use valueFn: instead.
All Widgets should have a functional example page.
(Not implemented) Widget example pages should follow the Example page Template.

Tests

The unit test suite should leave a clean DOM tree in between each test case.

Footnotes

[1] It looks like literal regexps confuse it, but OTOH, we recommend against using them.
Wrong, XmlLint rightly complains there is an unescaped less-than (<) in a document. Use != 0 or != 1 if you must embed script, but the right thing to do is to extract the script to a separate file.

== XmlLint notices ==

lib/lp/registry/templates/product-new.pt
    110: parser error : StartTag: invalid element name
    if (steps.search(/hidesearch/) < 0) {
    ^

[2] For example, if you want to toggle an element's visibility using POJS, use our unseen class:

    // Make this element invisible.
    element1.addClass('unseen');
    // Make this element visible again.
    element2.removeClass('unseen');

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