react-derive

For organizing and optimizing rendering of react components that rely on derived data. Works by wrapping your component in a HoC. For example, lets say your component shows the result of adding two numbers.

export default class Add extends Component {
  render() {
    const {a,b,fontSize} = this.props;
    return <div style={{fontSize}}>a + b = {a+b}</div>
  }
}

We can move the calculation of a+b to a decorator named @derive where we'll create the deriver function named sum. And because we named the function sum, the deriver's result will be passed into the Add component via a prop likewise named sum.

@derive({
  sum({a,b}) { return a+b }
})
export default class Add extends Component {
  render() {
    const {sum,fontSize} = this.props;
    return <div style={{fontSize}}>a + b = {sum}</div>
  }
}

Note that

• The first argument to a deriver function is newProps.
• The second argument is the previously derived props object (in this case it would look something like {a:5,b:3,sum:8})
• The value of this allows you to reference the result of other derivers like this.sum().

But wait, every time the component renders, sum will recalculate even if a and b didn't change. To optimize, we can memoize the calculation with @track so when the fontSize prop changes sum won't be recalculated.

@derive({
  @track('a', 'b')
  sum({a,b}) { return a+b }
})
export default class Add extends Component {
  render() {
    const {sum,fontSize} = this.props;
    return <div style={{fontSize}}>a + b = {sum}</div>
  }
}

We supply args 'a' and 'b' to the @track decorator to indicate that the sum deriver only cares about those two props. If fontSize changes, sum won't recalculate.

---

This project is similar to reselect for redux. However, while reselect helps manage derived data from global state, react-derive manages derived data from props.

@derive as a decorator

You can use this object to depend on other derived props:

@derive({
  @track('taxPercent')
  tax({taxPercent}) {
    return this.subtotal() * (taxPercent / 100);
  },

  @track('items')
  subtotal({items}) {
    return items.reduce((acc, item) => acc + item.value, 0);
  },

  @track('taxPercent')
  total({taxPercent}) {
    return this.subtotal() + this.tax();
  }
})
class Total extends React.Component {
  render() {
    return <div>{ this.props.total }</div>
  }
}

See the reselect version of the example above

Derive as a Component

options prop is the same as first argument to @derive. The child is a function that accepts the derived props object as it's first argument:

<Derive {...{taxPercent, items}} options={deriveOptions}>
{({tax, subtotal, total}) =>
  <ul>
    <li>tax: {tax}</li>
    <li>subtotal: {subtotal}</li>
    <li>total: {total}</li>
  </ul>
}</Derive>

ES6 support

Using ES7 decorators is in fact optional. If you want to stick with ES6 constructs, it's easy to do:

export const Add =
  derive({
    sum: track('a','b')
      (function({a,b}) { return a+b })
  })                                   // <--- function returned...
  (class Add extends Component {       // <--- immediately invoked by passing in class
    render() {
      const {sum,fontSize} = this.props;
      return <div style={{fontSize}}>a + b = {sum}</div>
    }
  });

See the examples/ dir of this repo for additional examples.

install + import

npm i react-derive -S

then:

import {Derive, derive, track} from 'react-derive';

or when included via script tag it's available as the global variable ReactDerive:

const {Derive, derive, track} = ReactDerive;

documentation

examples

• decorator demo: source - live demo
• component demo: source - live demo
• elegant-react-hot-demo (still a WIP)