A higher-order component for React to add computed or derived props to the wrapped component for better performance.
JavaScript
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README.md

react-computed-props

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A higher-order component for React to add computed or derived props to the wrapped component for better performance.

Installation

npm install --save react-computed-props

How do I use it?

To make use of React Computed Props, you just need two things:

  • a function that compute properties (e.g., computeProps(props))
  • a component that will receive the computed properties (e.g., MyComponent)

When you've got those, you just wrap your component with the addComputedProps higher-order component like so:

addComputedProps(computeProps)(MyComponent);

Here's a simple example demonstrating using computed props to find the minimum value in the data prop. By using addComputedProps, we can save ourselves from having to cycle through the whole dataset each time render is called, which can make a difference if you the dataset is large and render is called quite frequently (e.g., when handling mouse interaction events). The more expensive the computed props are, the more performance benefits you'll get from using addComputedProps.

import React, { Component, PropTypes } from 'react';
import addComputedProps from 'react-computed-props';

function computeProps(props) {
  const { data } = props;

  let minimum;
  if (data && data.length) {
    data.forEach((d) => {
      if (minimum == null || d < minimum) {
        minimum = d;
      }
    });
  }

  return {
    minimum,
  };
}

class DataSummary extends Component {
  static propTypes = {
    data: PropTypes.arrayOf(PropTypes.number),
    minimum: PropTypes.number,
  }

  render() {
    const { data, minimum } = this.props;

    return (
      <div className="DataSummary">
        <ul>
          <li>Data length: {data ? data.length : '--'}</li>
          <li>Minimum value: {minimum}</li>
        </ul>
      </div>
    );
  }
}

export default addComputedProps(computeProps)(DataSummary);

Examples

  • many-circles - An example of creating a visualization of 2000 circles with d3.

API Reference

addComputedProps(computePropsFunc, [options])(WrappedComponent)

Higher-order component that provides props computed in the computePropsFunc to the WrappedComponent. Unless alwaysRecompute is set, the computed properties will only be updated when the props it receives change. It takes the following options:

  • alwaysRecompute (Boolean): If true, always re-runs computedPropsFunc even if the props didn't change. Defaults to false.

  • changeExclude (String[]): If provided, changes to these props do NOT trigger re-running computedPropsFunc. Can't be used with changeInclude.

  • changeInclude (String[]): If provided, ONLY changes to these props triggers re-running computedPropsFunc. Can't be used with changeExclude.

  • flagRecomputed (Boolean): If true, includes a prop recomputedProps that is true if props were recomputed and false otherwise. Defaults to false.

  • recomputedFlagName (String): The name of the flag added to props indicating whether the props were recomputed or not, used when flagRecomputed is true. Defaults to 'recomputedProps'.

  • debug (Boolean): If true, prints to the console which props caused it to re-run computedPropsFunc. This is useful for ensuring only props you expect to be changing are changing.

Arguments
  1. computePropsFunc (Function): A function mapping from props to an object of computed props. These are used in addition to the regular props received when rendering WrappedComponent. If props contains keys that are also returned from computePropFunc, the values returned from computePropFunc will overwrite them.
  2. [options] (Object): The options object as described above.
  3. WrappedComponent (React Component): The component to inject the computed properties into as props.
Returns

A React component class

Remarks
  • Needs to be called twice addComputedProps(computePropsFunc, [options])(MyComponent).

Utility Functions

React Computed Props comes with three utility functions: compose, shallowEquals, and shallowEqualsDebug.

compose(...funcs)

A simple function that takes a list of functions and composes them. That is: compose(f, g, h)(foo) is the same as f(g(h(foo))). This can be potentially be used to chain multiple computed props functions together. For example:

export default compose(
  addComputedProps(visProps, { changeExclude: ['highlightPointId'] }),
  addComputedProps(highlightProps, { changeInclude: ['highlightPointId'] })
)(MyComponent);
shallowEquals(objA, objB, [excludeKeys], [includeKeys])

Returns true if objA (Object) shallow equals objB (Object). If excludeKeys (String[]) is provided, it ignores differences in the listed keys. If includeKeys (String[]) is provided, it only looks for differences in the listed keys. You cannot specify both excludeKeys and includeKeys.

shallowEqualsDebug(objA, objB, [excludeKeys], [includeKeys], [logPrefix])

Runs shallowEquals to see if objA shallow equals objB. If they do, it returns and logs the string 'equal'. If they do not, it returns and logs an array where each difference is logged in this format:

[keyName, objAValue, objBValue, ...]

This can be used to debug why shallowEquals returned false and to help ensure the props you are using are not mistakenly being recreated.

You can specify a prefix for the logging to console with the logPrefix argument, which defaults to 'shallowEqualsDebug'.

Sample output if the prop data changed from [1, 2] to [3, 4] and all other props stayed the same:

['data', [1, 2], [3, 4]]

If you see something like:

['data', [1, 2], [1, 2]]

It means you are re-creating an array and thus breaking performance benefits given by shallow equals comparing and aborting updates in shouldComponentUpdate.

Development

During development of examples, it can be helpful to have a watch running automatically rebuilding the package when changes take place. To get this running run:

npm run dev

Building

npm run build

Linting

npm run lint

To lint examples, run:

npm run lint:examples

Testing

npm run test

To test examples, run:

npm run test:examples

License

MIT