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magnetic declarative attributes

Snap together frontend and backend modules with html attributes.

2-way binding example

Everybody has 2-way binding examples, so here it is. Skip to the next example if you want to see something new.

Write some html and annotate the elements you want to bind with a special "binder" attribute:

<!doctype html>
      <input type="text" binder="yourName" placeholder="Enter a name here">
      <h1>Hello <span binder="yourName"></span>!</h1>
    <script src="bundle.js"></script> 

Just use attractor to scan the dom for the "binder" attributes, forwarding the elements into attr-bind:

var attractor = require('attractor');
var scope = { yourName: function (txt) { console.log(txt) } };
var attr = attractor({ 'binder': require('attr-bind') }, scope);

Bundle with browserify to generate the bundle.js:

$ browserify browser.js > bundle.js

Now load the html file in a browser and watch the span contents change as you edit the text box.


Data binding is a rather mundane application of what's possible with a basic attribute system in place. Let's go crazy and make a web app that renders in node and in the browser with page content that updates automatically whenever the database changes and full database access from the client!

This example is a work in progress. It will only get smaller as more modules are written.

First render some items server-side:

var http = require('http');
var fs = require('fs');
var ecstatic = require('ecstatic')(__dirname + '/static');
var hyperstream = require('hyperstream');
var feed = require('multilevel-feed');
var level = require('level');
var db = level('/tmp/lists.db', { encoding: 'json' });
var render = require('./render.js');
var server = http.createServer(function (req, res) {
    var m = /\/(\w+)*(\?|$)/.exec(req.url);
    if (!m) return ecstatic(req, res);
    var name = m[1] || 'default';
    var items = db.createReadStream({ start: 'item!', end: 'item!\uffff' });
    fs.createReadStream(__dirname + '/html/index.html').pipe(hyperstream({
        '#name': name,
        '#list': {
            _html: items.pipe(render()),
            'data-start': items._options.start,
            'data-end': items._options.end
var shoe = require('shoe');
var sock = shoe(function (stream) { stream.pipe(feed(db)).pipe(stream) });
sock.install(server, '/sock');

In our html, we'll add some attributes for the browser code to hook on to, declaratively:

    <link rel="stylesheet" href="/style.css">
    <h1 id="name"></h1>
    <div id="list" x-range="range"></div>
    <h2 class="hide">
      <span id="active" x-bind="active"></span>
      <button x-click="vote">vote</button>
    <form x-submit="addItem">
      <input name="title" type="text">
      <input type="submit" value="create">
    <script src="bundle.js"></script> 

Here is the browser code:

var attractor = require('attractor');
var observe = require('observable');
var render = require('./render.js');
window.db = require('multilevel-feed')();
var sock = require('shoe')('/sock');
function SortedList () { = observe(''); (txt) {
        if (!txt) return;
SortedList.prototype.range = function (xr) {
    var r = db.livefeed(xr.range).pipe(render());
    r.on('element', function (elem) { attr.scan(elem) });
    r.sortTo(xr.element, '.score');
}; = function (elem) {'.title').textContent);
SortedList.prototype.addItem = function (form, fields) {
    db.put('item!' + fields.title, { score: 0, title: fields.title });
}; = function (ev) {
    var key = 'item!' +;
    db.get(key, function (err, value) {
        value.score += 5;
        db.put(key, value);
var attr = attractor({
    'x-chooser': [ require('attr-chooser'), 'active' ],
    'x-bind': require('attr-bind'),
    'x-range': [ require('attr-range'), 'data-start', 'data-end' ],
    'x-submit': require('attr-submit'),
    'x-click': [ require('attr-ev'), 'click' ]
}, new SortedList);

The shared render.js rendering code is:

var hyperspace = require('hyperspace');
var fs = require('fs');
var html = fs.readFileSync(__dirname + '/html/item.html', 'utf8');
module.exports = function () {
    return hyperspace(html, { key: 'data-key' }, function (row) {
        return {
            '.title': row.value.title,
            '.score': row.value.score

and the html for the item.html is:

<div class="item" x-chooser="select">
  <div class="title"></div>
  <div class="score"></div>

We just made a live-updating application with shared browser and server rendering backed to leveldb in just 77 lines of javascript!

That is still too many lines, but it's getting there.


var attractor = require('attractor')

var attr = attractor(bindings, scope)

Return a new attractor instance attr.

bindings should map brace-expansion attribute names onto attribute handlers. Each binding will be added with .add().

Many attribute handlers are just modules with a function signature of:

module.exports = function (cb) {
    return function (elem) { /* ... call cb() somewhere in here... */ }

If you give an array instead of a function for the binding value, the first element will be taken as the function and the other elements will be bound as arguments to the function.

Modules that require extra arguments aside from cb should take their arguments before the cb. The cb goes last.

The scope is used to resolve the attribute values to functions. For example, for the html:

<div x-beep="boop"></div>

and an attractor binding on x-beep:

attribute({ 'x-beep': beeper }, scope)

When the <div> with x-beep is encountered, scope.boop() will fire with the arguments given to the callback inside the beeper module.

attr.add(attrName, fn)

Add an attribute from the brace-expansion of the string attrName. All of the attributes in the brace expansion must be present for the fn to apply.


Scan the dom node element for nodes matching


Attractor is not a framework. Instead, think of attractor as a minimal amount of glue necessary to let an ecosystem or autonomous declarative binding modules flourish, in the node.js spirit of tiny modules that do one thing well.

In furtherance of these goals, it's important that attractor modules should be trivial to reuse outside of attractor itself where possible.

find modules

Browse npm packages that have been tagged with the attractor keyword.

write an attractor module

To create a frontend attractor module, just provide a function that is compatible with the cb in attr.add(key, cb). It's usually advisable to wrap your function in an outside function to capture arguments from the user.

Here's a basic template you can use:

module.exports = function (cb) {
    return function (elem) {
        // call cb()` somewhere in here 

Inside your inner function, this will be set to the attractor instance attr. You should only rely on attr if your module actually needs access to the attribute instance. Otherwise, your module can enjoy a wider audience of people who aren't using attractor if you stick to the basic signature. However, some modules will need the attr instance such as modules that need to invoke the scan() to analyze new content.

Make sure to add a keyword in your package.json for "attractor" so that people will know how to find your module.

If you also name your frontend module starting with attr- then people can assume that it was built for attractor compatibility and they will have an easier time finding it, but this isn't strictly necessary.

For an example of a frontend attractor module, look at the attr-bind module.


With npm do:

npm install attractor