A view library for building and styling web components in pure-javascript.

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"Modular, composable web components. Modular, composable styles." gem Gem.js is a view library - a set of extensible web components for building visual user interfaces and styling web applications in pure-javascript. The power of functions and variables is unparalleled, and yet languages like HTML and CSS, which don't have any ability to compose structures together, are still the primary ways people build web applications. Framework after framework has come along to try and solve the problem of making web pages dynamic. Angular, Backbone, Ember, jQuery, mooTools, Dojo, YUI, etc have all tried to be everything to everyone. But what they fail at providing is simplicity and modularity. They end up with bloated libraries filled with features you're not using. Gem.js is here to change that. Finally, modern application development for the browser! - Gem
- [Static properties and methods](#static-properties-and-methods)
- [Instance properties and methods](#instance-properties-and-methods)
- [Event instance properties and methods](#event-instance-properties-and-methods)
- [`ifon`](#ifon)
- [`proxy`](#proxy)
- [Instance events](#instance-events)
- [Dom Events](#dom-events)
- Custom Gems
- [Releasing custom gems as separate modules](#releasing-custom-gems-as-separate-modules)
- [Inheriting from Gems with a class library other than `proto`](#inheriting-from-gems-with-a-class-library-other-than-proto)
- [Inheriting from Gems without a class library](#inheriting-from-gems-without-a-class-library)
- Standard Gems
- [Conventions](#conventions)
- [Button](#button)
- [Canvas](#canvas)
- [CheckBox](#checkbox)
- [Block](#block)
- [Image](#image)
- [List](#list)
- [Radio - Not a `Gem`](#radio---not-a-gem)
- [Select](#select)
- [Svg](#svg)
- [Table](#table)
- [Text](#text)
- [TextArea](#textarea)
- [TextField](#textfield)
- Style objects
- [`Style` constructor](#style-constructor)
- [`<cssPropertyName>`](#csspropertyname)
- [`$setup` and `$kill`](#setup-and-kill)
- [`$state`](#state)
- [`<GemName>`](#gemname)
- [`$<label>`](#label)
- [`$$<pseudoclass>`](#pseudoclass)
- [`$inherit`](#inherit)
- [Combining them together](#combining-them-together)
- [`styleObject.mix`](#styleobjectmix)
- [`styleObject.copy()`](#styleobjectcopy)
- [`Style.addPseudoClass`](#styleaddpseudoclass)
- [`styleObject.toString`](#styleobjecttostring)
- [`Style.fromString`](#stylefromstring)
- [`styleObject.toObject`](#styleobjecttoobject)
- [Standard Pseudoclasses](#standard-pseudoclasses)
- [Built-in JS Rendered Pseudoclasses](#built-in-js-rendered-pseudoclasses)
- [Default style](#default-style)
- Tips and Recommendations
- [Don't Create a node until you need it](#dont-create-a-node-until-you-need-it)
- Other Gem Modules Example ======= ```javascript var Button = require("gem/Button") var Style = require("gem/Style") var Block = require("gem/Block") var list = Block() ;1,2,3.forEach(function(n) {
var text = "Hi "+n
var toggleButton = Button(text) // create a button
// make it do stuff when you click on it
toggleButton.on('click', function() {
if(toggleButton.text !== "RAWRR!!!") {
toggleButton.text = "RAWRR!!!"
toggleButton.state.set('color', 'rgb(128, 0, 0)')
} else {
toggleButton.text = text
toggleButton.state.set('color', 'black')
// add the button to the list
}) var greet = Button("send", "Send your Greetings") // labels like 'send' can differentiate
// otherwise identical types of gems
list.add(greet) // create styles with style objects .. = Style({
border: '1px solid blue', // .. that use familiar css values,
marginRight: 34,          // .. camelCase css properties and integers interpreted
//    as "px" values when appropriate,
Button: {                 // .. sub-gem styles,
$$firstChild: {       // .. pseudo-class styles,
color: 'rgb(0,100,240)',
$state: function(state) { // .. more sophisticated styling techniques
return Style({
color: state.color
$send: {              // .. style based on an object's label, and ..
color: 'green'
}) // append the list of buttons to the document body (so it shows up) list.attach() // custom gems (use your favorite javascript class library - here proto is being used) var NameInput = proto(Gem, function() { // inherit from Gem = 'NameInput' = function(LabelText) {  // the `build` method initializes the custom Gem
this.nameField = TextField()
this.add(Text(LabelText), this.nameField)
this.nameField.on('change', function() {
list.children[0].text = "Hi "+this.val
}) var nameInput = NameInput("Your Name: ") greet.on('click', function() {
var text = Text("Whats up, "+nameInput.nameField.val+'?') = Style({display:'block'})
}) nameInput.attach() ``` example If anything in the documentation is unclear, or you want to see more examples, the unit tests give a comprehensive and exhaustive set of examples to look at. Why use Gem.js? ====================
  • Makes your web application easier to develop with modular reusable structure objects (Gem objects) and Style objects
  • No HTML Needed. With Gem.js, you write in 100% javascript. The only html requirement is a document body. You can still add plain old HTML into your gems using gem.domNode.innerHTML tho if you so choose.
  • No CSS Needed. While Gem.js uses css style properties, it rejects the cascading nature of css, allowing one style to be fully isolated from another. No more wondering which selector in which stylesheet botched your nice clean style.
  • Works with your HTML and CSS. Gems can be added as a child to any standard dom object and they can be styled with standard css stylesheets if you so choose.
  • Works with your current javascript. Gems give you direct access to their domNode so you can use the dom manipulation libraries you're used to.
  • Fully separate style from structure. By using $state, $setup, and $kill javascript in your Style objects, you can include any javascript that is stylistic rather than structural.
  • Import Gem modules with real APIs that anyone can release online. HTML snippets are so 1995.
  • Lowers your risk of Cross-Site scripting. Data in Gem.js doesn't need to be escaped, and so you can cross that off your worry-list.
  • Has a small footprint: 16.5KB minified and gzipped in umd format
Comparisons =========== Install ======= ``` npm install gem ``` or download the built package Gem.umd.js from the 'dist' folder in the repository Usage ===== ```javascript var Gem = require('gem') // node.js and webpack define('Gem.umd.js', function(gem) { ... } // amd ``` Gem ------ All gems inherit from Gem - the basic building-block of the system. Gems are EventEmitters, and emitting events is one of the primary ways gems should communicate. Gem is abstract and can't be instantiated on its own. See the section ''Custom Gems'' for details on how to create objects that inherit from Gem.

Static properties and methods - The name of the Gem. Used both for naming dom elements for view in browser dev tools and for styling. Gem.attach(listOfGems) - Appends the passed gems to document.body. IMPORTANT: only attach a gem to the dom via this attach function or a gem's attach/attachBefore method. Without this, styles won't be rendered. \ Gem.attach(domNode, listOfGems) - Appends the passed gems to the passed domNode. \ Gem.attachBefore(domNode, listOfGems) - Appends the passed gems before the passed domNode as a sibling. Gem.detach(listOfGems) - Removes the passed gems from their respective dom parents. Gem.createBody(callback) - Dynamically creates the body tag. Calls callback when done. - (Default: false) - When set to true, certain debugging feature are enabled.

Instance properties and methods

gem.parent - The Gem's parent (which will also be a Gem) \ gem.children - An array of the Gem's children (which will all be Gems themselves). \ gem.domNode - The Gem's standard dom node object. \ gem.label - A string used for styling. Should be set once when the object is instantiated, and cannot change. See the section on Style objects for details about how this is used. \ gem.excludeDomEvents - A set of dom events to exclude from automatic registration. Will have the structure {eventName1:1, eventName2:1, ...}. See the documentation for on for more details. \ gem.state - An observer object that can be listened on for changes. Can be used for any purpose, but is intended for being used to create dynamically changing styles. See the section on Style objects for an example. gem.add(gem, gem, ...) - Appends gems as children to the calling gem. This causes the domNodes of the passed gems to be appended to the calling gem's dom node. \ gem.add(listOfGems) - Same as above, but listOfGems is an array of Gem objects. gem.addAt(index, gem, gem, ...) - Adds gems as children to the calling gem at a particular index. \ gem.addAt(index, listOfGems) - Same as above, but listOfGems is an array of Gem objects. gem.addBefore(beforeChild, gem, gem, ...) - Adds gems as children to the calling gem before a particular child. If beforeChild is undefined, this will append the given nodes. \ gem.addBefore(beforeChild, listOfGems) - Same as above, but listOfGems is an array of Gem objects. gem.remove(gem, gem, ...) - Removes the passed gems as children. \ gem.remove(listOfGems) - Same as above, but listOfGems is an array of Gem objects. \ gem.remove(index, index, ...) - Removes, as children, the gems at the given indexes in the children list. \ gem.remove(listOfIndexes) - Same as above, but listOfIndexes is an array of indexes to remove. gem.attach(domNode=document.body) - Appends this Gem's domNode to the passed domNode (default document.body). IMPORTANT: only attach a gem to the dom via the attach function or a gem's attach/attachBefore method. Without this, styles won't be rendered. \ gem.attachBefore(domNode=document.body) - Appends this Gem's domNode before the passed domNode (as a sibling). gem.detach() - Removes this Gem's domNode from its dom parent. gem.attr(attributeName) - Return the value of the attribute named attributeName on the Gem's domNode. \ gem.attr(attributeName, value) - Sets the attribute to the passed value. \ gem.attr(attributeObject) - Sets the attributes in the attributeObject, where attributeObject looks like: {attribute1: value1, attribute2: value2, ...}. - Holds the object's Style object. Starts out undefined, and can be set to undefined to remove a Style that has been set. Changing this property triggers style affects in the Gem's children. \ gem.visible - Setting this variable to false hides the gem using "display: none;". Setting this variable to true unhides it. Accessing the variable will return its visibility state. \ gem.focus - Setting this variable to true gives the gem focus on the page. Setting this variable to false blurs it. Accessing the variable returns whether or not the gem is the focused element on the page. \ gem.quiet.focus - Just like gem.focus but won't cause a "focus" or "blur" event. gem.selectionRange - Returns an array representing the selection range in terms of visible character offsets. E.g. a value of [2,4] means that the current element has 2 visible entities (usually characters) selected within it at offset 2 and 4 from the start. Note that if there are hidden characters like multiple spaces in a row, or newlines, or other non-visible characters (mostly only applies to contenteditable nodes), they are ignored. \ gem.selectionRange = [offsetStart, offsetEnd] - Setting the selectionRange property sets the selection inside the Gem's domNode based on the given offsets. Example of selectionRange: ```javascript var x = Text("You're not my buddy, guy") x.attach() x.selectionRange = 0,6 // selects "You're" ```

Event instance properties and methods

Most of these are inherited from EventEmitter. All methods and properties from EventEmitter are inherited by Gem. The important ones: gem.emit(event, data, data2, ...) - Emits an event that triggers handlers setup via the Gem's on methods. gem.on(event, callback) - Registers a callback that will be called when the passed event is emitted by the Gem. \
  • event - The string event name to listen for. If the passed event is one of the many standard dom events (e.g. 'click', 'mouseover', 'touchstart', etc), the passed handler will be registered as a dom event handler in one of three cases:
* the gem's `excludeDomEvents` object is undefined
* the event is `in` the gem's `excludeDomEvents` property
  • callback(data, data2, ...) - the callback gets any arguments passed to emit after the event name.
gem.onCapture(event, callback) - Just like gem.on but listens on the capture phase of native browser events. Note: this doesn't currently listen on events that aren't native browser events. gem.once(event, callback) - Like on but the callback will only be called the first time the event happens., callback) - Removes a callback as an event handler (the callback won't be called for that event again). gem.removeListener(event,callback) - Same as off. gem.removeAllListeners(event) - Removes all the callbacks for the passed event, except capture handlers. gem.removeAllListeners() - Removes all callbacks except capture handlers. gem.offCapture(event, callback) - Removes a capture handler.
The ifon and related methods are useful primarily for performance reasons. They allow registering event listeners only when they're needed, so that the browser doesn't get overloaded with event handlers. Its recommended that ifon is used whenever possible. An example: ```javascript var text = Text("CLICK ME") var parent = Block(text) var handler; parent.ifon('someoneClickedTheThing', function() {
text.on('click', handler = function() {
parent.emit('someoneClickedTheThing', "I can't believe it")
}) parent.ifoff('someoneClickedTheThing', function() {'click', handler)
}) ``` gem.ifon(event, callback) - Registers a callback that will be called when a handler is registered for event if it had no handler registered previously. If there is already a listener attached to that event, callback is called immediately. \ gem.ifon(callback) - Registers a callback that will be called when the first handler for any event is registered.
    • callback(event) - The callback gets the newly registered event type as its argument.
gem.ifoff(event, callback) - Registers a callback that will be called when the last handler for event is unregistered. \ gem.ifoff(callback) - Registers a callback that will be called when the last handler for any event is unregistered.
  • callback(event) - The callback gets the unregistered event type as its argument.
gem.removeIfon() - Removes all ifon handlers. \ gem.removeIfon(event) - Removes all ifon handlers for the passed event. \ gem.removeIfon(callback) - Removes callback as an "all" ifon handler (a callback passed to ifon without an event). \ gem.removeIfon(event, callback) - Removes callback as an ifon handler for the passed event. gem.removeIfoff() - Removes all ifoff handlers. \ gem.removeIfoff(event) - Removes all ifoff handlers for the passed event. \ gem.removeIfoff(callback) - Removes callback as an "all" ifoff handler (a callback passed to ifoff without an event). \ gem.removeIfoff(event, callback) - Removes callback as an ifoff handler for the passed event.
The proxy method uses ifon and ifoff to minmize the number of event listeners that need to be attached in the system. gem.proxy(emitter, options) - Proxies event registration to emitter. \
  • emitter - The emitter (usually a Gem) to proxy handler binding to \
  • options - An object that defines what events are proxied. If undefined, all events are proxied. The object can have one of the following properties:
only - An array of events to proxy. except - An array of events to not proxy. All other events are proxied. Example of proxy: ```javascript var A = Text() var B = Text() A.proxy(B) A.on("click", function(x) {
console.log("hey hey heyyy! "+x)
}) B.emit("click", "Ughh..") // console prints "hey hey heyyy! Ughh.." ```

Instance events

"attach" - Emitted when the gem is attached to the document. \ "detach" - Emitted when the gem is detached from the document. \ "newParent" - Emitted when a Gem gets a new parent. Note: this event is used by Style objects, so don't prevent these events. \ "parentRemoved" - Emitted when a Gem is detached from its parent. Note: this event is used by Style objects, so don't prevent these events. \

Dom Events

Gem object will emit any standard dom event ("click", "mousedown", "keypress", etc) when listened on. Note that a Gem doesn't add an event listener to the dom node until someone listens on that event on the gem. This minimizes the number of event listeners that are registered on the page. To see the list of dom events this applies to (supposed to be all of them), see the top of src/nodemodules/Gem.js Custom Gems ------------- Gem.js is all about custom components. That's the point: your application should be built as a composition of custom gems on top of custom gems so that, instead of a million divs, you have semantically appropriate javascript web components. In this documentation, we're going to be using the class library proto. The descriptions here apply to both inheriting from Gem and inheriting from any of the standard gems. There are a couple special properties to create when making a custom Gem:
  • name - The name is a required property, should be named whatever your class is named, and should be a somewhat unique name in your system (tho it isn't required to be unique).
  • build() - The "sub-constructor". The constructor calls this method, passing all arguments, to the build method. The return value of build is ignored.
  • defaultStyle - If set to a Style object, the style object will be the gem's default style. Unlike explicitly set Styles and inherited Styles, css properties in defaultStyle do cascade line-by-line. Also, if a gem inherits from another Gem class that also has a defaultStyle, the default styles mix together with the child Gem class style properties overriding the parent Gem class's default properties. So in the below example, if gem is given a style that defines color: green, it's fontWeight will still be 'bold'.
For example: ```javascript var CustomGem = proto(Gem, function() { = "CustomGem"
this.defaultStyle = Style({
color: 'red',
fontWeight: 'bold'
}) = function(x) {
this.x = x
}) var gem = CustomGem(5) // gem.x is 5 ```

Releasing custom gems as separate modules

If you'd like to release a custom Gem or set of Gem objects, there are a couple of important things to remember to do:
  • If you're releasing on npm, do not add Gem.js as a normal "dependency". Instead, it should be added as a "peerDependency" or perhaps a "devDependency". It shouldn't be a normal "dependency" because otherwise bundlers may bundle multiple copies of Gem.js when using your custom gem module (even though bundlers like webpack dedupe files, if the versions of webpack being used are slightly different, they would still package together both versions of Gem.js)
  • If you're releasing a module distribution intended to be loaded in a <script> tag, do not bundle Gem.js in your distribution bundle. It should assume the gems global variable (e.g. gems.Gem) is available.

Inheriting from Gems with a class library other than proto

If you're building Gems with something other than proto (or are using a version of proto older than 1.0.17), note that Gem.js relies on the following properties:
  • gem.constructor - must point to the Gem prototype class (in the proto example, the object returned by the call to proto). This is a standard property that all good class libraries should set.
  • gem.constructor.parent - must point either to the parent of the gem's constructor, or undefined if there is no parent. Note that while proto sets this automatically, it is not a standard property and if you're using a different library from proto, you must set this manually.
  • - the constructors must have the same name property that instances can access. Note that while proto sets this appropriately, most class libraries probably don't and it isn't simple to manually set. See here for details.
Also, make sure that Gem's constructor is called on new instances that inherit from Gem.

Inheriting from Gems without a class library

Properly subclassing a prototype in javascript isn't the simplest thing to do, but if you want to do it, here's how: ```javascript var CustomGem = function() { // Gem's constructor must be called
} CustomGem.parent = Gem // needed for correct Style rendering var Intermediate = function(){}; Intermediate.prototype = Gem.prototype CustomGem.prototype = new Intermediate() = 'CustomGem' // the name is a required property CustomGem.prototype.constructor = CustomGem // required for correct Style rendering,
// and is a standard javascript convention = function(constructorArgument1, constructorArgument2, ...) {
// .. custom constructor code
} CustomGem.prototype.customMethod = function() {
// ...
} ``` Standard Gems --------------- The built-in standard gems all inherit from Gem and so have all the methods and properties in the above documentation. For each build-in gem, its name property will be the same as the name the documentation uses for it. For example Button will have the name "Button". To use these built in gems, access them via either require("gem/<GemName>") or Gem.<GemName>. For example: ```javascript var Table = require("gem/Table") // webpack or browserify // or var Table = Gem.Table // if loading the umd bundle in a