linkState

Create an Event handler function that sets a given state property. Works with preact and react.

Tiny: ~300 bytes of ES3 gzipped
Familiar: it's just a function that does what you would have done manually
Standalone: one function, no dependencies, works everywhere

🤔 Why?

linkState() is memoized: it only creates a handler once for each (key, eventPath) combination.

This is important for performance, because it prevents handler thrashing and avoids allocations during render.

Installation

npm install --save linkstate

The UMD build is also available on unpkg:

<script src="//unpkg.com/linkstate/dist/linkstate.umd.js"></script>

This exposes the linkState() function as a global.

How It Works

It's important to understand what linkState does in order to use it comfortably.

linkState(component, statePath, [valuePath])

component: the Component instance to call setState() on
statePath: a key/path to update in state - can be dot-notated for deep keys
valuePath: optional key/path into the event object at which to retrieve the new state value

It's easiest to understand these arguments by looking at a simplified implementation of linkState itself:

function linkState(component, statePath, valuePath) {
  return event => {
    let update = {};
    update[statePath] = event[valuePath];
    component.setState(update);
  };
}

In reality, accounting for dot-notated paths makes this trickier, but the result is the same.

Here's two equivalent event handlers, one created manually and one created with linkState:

handleInput = e => {
  this.setState({ foo: e.target.value })
}

handleInput = linkState(this, 'foo')

Notice how we didn't specify the event path - if omitted, linkState() will use the checked or value property of the event target, based on its type.

Usage

Standard usage is a function that returns an event handler to update state:

import linkState from 'linkstate';

class Foo extends Component {
  state = {
    text: ''
  };
  render(props, state) {
    return (
      <input
        value={state.text}
        onInput={linkState(this, 'text')}
      />
    );
  }
}

You can also use it as a polyfill. This emulates the behavior of Preact 7.x, which provided linkState() as a method on its Component class. Since you're then calling linkState() as a method of the component instance, you won't have to pass in component as an argument:

import 'linkstate/polyfill';

// Component.prototype.linkState is now installed!

class Foo extends Component {
  state = {
    text: ''
  };
  render(props, state) {
    return (
      <input
        value={state.text}
        onInput={this.linkState('text')}
      />
    );
  }
}

Contribute

First off, thanks for taking the time to contribute! Now, take a moment to be sure your contributions make sense to everyone else.

Reporting Issues

Found a problem? Want a new feature? First of all see if your issue or idea has already been reported. If it hasn't, just open a new clear and descriptive issue.

Submitting pull requests

Pull requests are the greatest contributions, so be sure they are focused in scope, and do avoid unrelated commits.

💁 Remember: size is the #1 priority.

Every byte counts! PR's can't be merged if they increase the output size much.

Fork it!
Clone your fork: git clone https://github.com/<your-username>/linkstate
Navigate to the newly cloned directory: cd linkstate
Create a new branch for the new feature: git checkout -b my-new-feature
Install the tools necessary for development: npm install
Make your changes.
npm run build to verify your change doesn't increase output size.
npm test to make sure your change doesn't break anything.
Commit your changes: git commit -am 'Add some feature'
Push to the branch: git push origin my-new-feature
Submit a pull request with full remarks documenting your changes.

License

MIT License © Jason Miller