Experimenting with Express: Node.js day two
Day one was figuring out how to install node, express, and npm on Ubuntu and to get it to work, as well as some furtive experiments with a DIY module. Now I am trying to get Epress to do things my way.
I have three goals for buggering with Express:
- Figuring out what a module is in the whole Node.js framework
- Figuring out how to pass information around inside Node, and templates
- Trying to figure out why I always pre-designate how many items I want in a list before writing them out
Add a breadcrumb to the MVC example of express
express has a default page layout file, views/layout.html; in the mvc example, as in most of the examples, body is inserted inside an HTML layout. I want to add a 'breadcrumb' variable and insert it into the layout as in:
<html>
<head>
<title>Express - MVC Example</title>
<link rel="stylesheet" href="/style.css" />
</head>
<body>
<% if (breadcrumb) { %><div id="breadcrumb"><%- breadcrumb %></div>
<% } else { %>No Breadcrumb<% } %>
<%- body %>
</body>
</html>
body is a special layout variable - the first value passed to res.render is set as the body. Where do you get any other layout variables you want to send to a layout? That's what the second (often omitted ) object is for.
For instance, for the example above to work every render has to be written as
res.render('my body', {breadcrumb: foo});
There may be another way to seed all responses with a default value but in this case, its kind of okay that each response needs a new breadcrumb value, becuase you kind of want a custom breadcrumb for each url responder anyway.
Creating a breadcrumb handling library
Although you could hand code each and every breadcrumb, I want a little more elegance so I write a breadcrumb library to have relevant functions and constants. Actually I want it to put some constants into the global space without reference to the module. To do that I take advantage of the global variable called 'global'. This is a little confusing; in node.js global is a value that when found in a module, transfers all values attached to it to the global space. It may be a CommonJS feature - not sure; but the upshot is that when you write a module - as in my init.js module - as such
global.BC_HOME = '<a href="/">HOME</a>';
global.BC_SEP = ' ~ ';
exports.link = function (ref, text, opts){
return '<a href="' + ref + '">' + text + '</a>';
}
you can then use the values BC_HOME and BC_SEP in any module that requires 'init'. as in:
var init = require('./../init');
...
module.exports = {
// /users
index: function(req, res){
req.breadcrumb = 'bc_req';
res.render(users, {breadcrumb: BC_HOME + BC_SEP + 'users'});
},
// /users/:id
show: function(req, res, next){
get(req.params.id, function(err, user){
if (err) return next(err);
res.render(user, {breadcrumb: BC_HOME + BC_SEP
+ init.link('/users', 'users') + BC_SEP + 'show'});
});
},
The above example also has a function 'link' that is used in the second function in the object block. Because it is attached to exports, it must be referred to from the module object by name.
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