elem-simple

Super simple version of elemjs, under 300 loc and around 3,5Kb gzipped, with absolutely no runtime dependencies.

npm install --save elem-simple

or import the script from npmcdn with

<script src="https://npmcdn.com/elem-simple/dist/elem.js"></script>

Basics

the Elem API is pretty simple

• Elem.createElement(name, props, ...children): create the representation of a DOM node(called an element below). Used by JSX expressions.
• Elem.render(tree, node, append = false): render the tree of elements into the node
• Elem.renderToString(tree): return an HTML string representation for the tree of elements
• Elem.Component : Component class to subclass

you can use it this way

import Elem from 'elem-simple';
 
// a simple Hello component
const Hello = ({ who = 'World' }) => <h1>Hello {who}! ({Date.now()})</h1>;
 
// an app that uses the Hello component
const App = () => <div><Hello who="Mathieu" /></div>;
 
// render the App function inside the DOM
const app = Elem.render(<App />, document.getElementById('app'));
 
// redraw the App function every second
const interval = setInterval(app.redraw, 1000);
 
// after 5 seconds, cleanup everything
setTimeout(() => {
  clearInterval(interval);
  const actualDOMNodeOfApp = app.getNode();
  ...
  app.cleanup(); // remove app nodes from the DOM
}, 5000);

JSX support

elem comes with builtin JSX support through createElement function.

You can either provider a jsx pragma to Babel

// .babelrc
{
  "presets": ["stage-0", "es2015", "react"],
  "plugins": [
    ["transform-react-jsx", { "pragma": "Elem.createElement" }]
  ]
}

import Elem from 'elem-simple';
 
const App = ({ who = 'World' }) => <h1>Hello {who}!</h1>;
 
Elem.render(<App who="Mathieu" />, document.getElementById('app'));

or provide a fake React context

import { render, createElement } from 'elem-simple';
 
const React = { createElement };
const ReactDOM = { render };
 
const App = ({ who = 'World' }) => <h1>Hello {who}!</h1>;
 
ReactDOM.render(<App who="Mathieu" />, document.getElementById('app'));

Functions as tags (or stateless components)

As you may have noticed, the first argument of Elem.createElement is either a string, a function that return a JSX tree or a subclass instance of Elem.Component.

import Elem from 'elem-simple';
 
const Item = ({ name = '--' }) => <li>{props.name}</li>;
const App = (props) => <ul>{props.who.map(item => <Item name={item} />)}</ul>;
 
Elem.render(<App who={['John', 'Jane']} />, document.getElementById('app'));

Classes as tags or stateless components

import Elem from 'elem-simple';
 
class App extends Elem.Component {
  constructor(props) {
    super(props);
  }
  getDefaultProps() {
    return {
      who: 'World',
    };
  },
  render() {
    return (
      <h1>Hello {this.props.who}!</h1>
    );
  }
}
 
Elem.render(<App who="Mathieu" />, document.getElementById('app'));

Properties

Whenever you use a function as a JSX tag, a props object is passed along. In this props object you will find any parameters passed to the JSX node and the following properties :

• props.children : the children of the tag
  • const list = <List><li>Hello</li></List>
• props.redraw : if you pass a function reference to Elem.render then any call to redraw from any function element inside the tree will trigger a new Elem.render of the same function
• props.myself
  • getNode() : get the root node returned by the current function
  • redraw(props) : redraw the root node returned by the current function with the same element and different props
  • replaceWith(element) : replace the root node returned by the current function with another element
• props.treeContext : a plain old javascript object common to the whole tree. You can put whatever you need inside and you are responsible for it's management

So when you are passing properties to a functional element, avoid to name your properties with the following values

• children
• redraw
• myself
• treeContext

SVG support

 
import Elem from 'elem-simple';
 
const shapes = (
  <svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="300" height="200">
    <rect width="100" height="80" x="0" y="70" fill="green" />
    <line x1="5" y1="5" x2="250" y2="95" stroke="red" />
    <circle cx="90" cy="80" r="50" fill="blue" />
  </svg>
);
 
Elem.render(shapes, document.getElementById('app'));

Inline styling

You can use plain old javascript object to define inline style on your HTML nodes

const style = {
  color: 'red',
  backgroundColor: 'black',
  fontSize: '29px',
};
const node1 = <div style={style}>Hello</div>;

CSS classes support

When you have to provide one or more classes on an HTML element, you can do it the following ways. Don't forget to use className instead of class.

const node1 = <div className="hello">Hello</div>;
const node2 = <div className="hello hello-green">Hello</div>;
const node3 = <div className={['hello', 'hello-green']}>Hello</div>;
const node4 = <div className={{ hello: true, helloGreen: true, helloBlack: false }}>Hello</div>;

Universal render

import Elem from 'elem-simple';
 
const App = ({ who = 'World' }) => <h1>Hello {who}!</h1>;
 
const htmlCode = Elem.renderToString(<App who="Mathieu" />);
 
console.log(htmlCode);

DOM nodes references

Whenever you need to get the actual DOM node behind a JSX node, you can provide a ref callback

let textinput;
 
const Component = (props) => {
  return (
    <div>
      <input type="text" ref={(n) => textinput = n} />
      <button type="button"
        onClick={() => console.log(textinput.value)}>
        redraw
      </button>
    </div>
  );
};

Specs

• JSX first class support through Elem.createElement
• you can attach event handlers on any DOM element with a function as property called onEventname
• reusable components are done via plain old functions
  • each call to these functions are made by the library
  • the call to these functions is deferred until the library need to render it to the DOM or elsewhere
  • the first and only argument of the function is the properties of the element
  • the properties contains a special attribute (children) that represents the array of children of the element. Can be empty
  • the properties contains a special attribute (redraw) that allow the user to re-render the whole element tree passed to Elem.render
  • the properties contains a special attribute (myself) that contains informations about the physical place in DOM where the element tree of the function will be inserted
    • myself has a function called getNode that returns the root node return by the function
    • myself has a function called redraw that recall the original function with new properties and renders it at the same place
    • myself has a function called replaceWith that renders it a new element tree at the same place
  • if you define the property className (the class) it can be
    • a simple string
    • an array of string
    • an object with boolean values. Each key with a true value will be added to the class
  • if you define the property style it can be
    • a simple string
    • an object that will be serialized to a style value
  • if you define the property ref on a DOM element as a function, this function will be called with the actual DOM node created by Elem as the first parameter of the function
• reusable components are also done via classes that extends Elem.Component with a render method. props are available through this.
• Elem.render can render an element tree, or an array of element tree created with Elem.createElement
• Elem.render takes an HTMLElement as second parameter
• Elem.render can take a third parameter to specify if the element tree will be appended to the root node of if the content of the root node will be deleted. By default, it's deleted
• Elem.renderToString return a string output of the element tree
• Elem.renderToString doesn't need to be called inside a browser env
• Elem can render SVG nodes
• if you pass an attributes object on an HTML element, all the values of the object will be directly set on the actual DOM node. Works for stuff like innerHTML, indeterminate, etc ...