Purely functional data binding for React

Lightweight (6.5K minified) purely functional two-way data binding for the React designed for TypeScript and ES6.

While losely based on the original React Link idea, valuelink develops the idea further providing simple and elegant solutions for many common problems, such as data binding of the complex state elements and form validation.

Introductory tutorials explaining the basics of the 'Value Link' pattern:

• Managing state and forms with React. Part 1
• Managing state and forms with React, Part 2: Validation
• State and forms in React, part 3: Managing Complex State

Examples are here

Features:

• Support for all major data binding scenarios, including radio groups and select lists.
• Declarative form validation.
• Easy handling of the complex React state with nested objects and arrays.
• 'pure render' optimization friendly due to the value links caching.
• Exact type inference with the TypeScript.

Reference implementation of 'linked' UI controls included (tags.jsx).

• Standard tags: <Input /> and <TextArea /> (with validation), <Select />,
• Custom tags: <Radio />, <Checkbox />, <NumberInput />

This technology is one of the key components of NestedReact architecture, helping you to build large-scale React applications with a powerful and fast NestedTypes classical OO models.

New in 1.4

• (!) link.remove( key ) is renamed to link.removeAt( key ); link.remove() will work as usual for the links to array/object elements.
• New ES6 API for value links creation:
  • Extend the LinkedComponent base class instead of React.Component.
  • Use this.linkAt( 'stateKey' ) instead of Link.state( this, 'stateKey' ).
  • Use this.linkAll( 'key1', 'key2', ... ) instead of Link.all( this, 'key1', 'key2', ... ).
  • this.linkAll() without arguments will link each member of the state.
  • New API is precisely typed with the recent TypeScript features. this.linkAt( 'a' ) will cause compilation error if 'a' is not a member of the state. Generated links are properly typed as well.
• Support for modern bundlers in the package.json (module field points to lib folder with transpiled ES6-import modules).
• UMD module is included in dist folder (exporting NestedLink global variable).
• Updated examples.

Installation

To use in your project

npm install valuelink

Both UMD and ES6-imports modules are available. MIT License. No side dependencies.

// Links
import React from 'react'
import Link, { LinkedComponent } from 'valuelink'

// You'll need this components with React 15.x instead of standard ones.
import { Input, TextArea, Select, Radio, Checkbox } from 'valuelink/tags.jsx'

tags.jsx intended to be starting boilerplate for your custom components. Copy this file to your project, and start hacking.

To start hacking

If you want to play with the examples, fix the bug, or whatever:

npm install - installs the dependencies.

npm run build - compiles everything including examples.

To create your custom data binding

It's really straightforward. Look at the component.ts file to see how binding to React state is implemented, it should be a good start. Basically, all you need is to subclass React.Component and make your own linkAt and linkAll methods. You can either use Link.value inside to create links dynamically, or extend the Link as it's done there.

How to

Create link

Links can be created and used inside of the React component.render() method.

Linking to the state attributes

LinkedComponent.linkAt( stateKey ) : Link

Create link to an attribute of the component's state. Component must extend LinkedComponent class.

Can be overriden to create custom data binding for something different than the React state.

const nameLink = this.linkAt( 'name' ),
      emailLink = this.linkAt( 'email' );

LinkedComponent.linkAll( stateKey1, stateKey2, ... ) : { [ key ] : Link }

Create an object with links to listed state members. When no keys are provided, it creates link to every member of the state. Component must extend LinkedComponent class.

Can be overriden to create custom data binding for something different than the React state.

const links = this.linkAll( 'name', 'email' ),
      { name, email } = links;

Link.state( this, stateKey ) : Link

Same as component.linkAt(), but works with any component class.

const nameLink = Link.state( this, 'name' ),
      emailLink = Link.state( this, 'email' );

Link.all( this, stateKey1, stateKey2, ... ) : { [ key ] : Link }

Same as component.linkAll(), but works with any component class.

const links = Link.all( this, 'name', 'email' ),
      { name, email } = links;

this.links : { [ key ] : Link }

All links created during render() are cached inside the component.link object. Direct access to the cache may be used in event handlers to reference these links.

When you create the link to the value which has not been changed since the last render, link object will be reused. Which means that it's safe to use pure render optimization.

Links to object and arrays

linkToObject.at( key ) : Link

Create link to the member of array or object.

If linked value is plain object or array, it's possible to generate links to their members. Whenever this derivative links will be updated, it will lead to proper purely functional update (with shallow copying) of the parent element.

const deepLink = this.linkAt( 'array' ).at( 0 ).at( 'name' );
deepLink.set( 'Joe' ); // Will update component state.array

linkToObject.pick( key1, key2, ... ) : { [ key ] : Link }

Create links to the object's members, and wrap them in an object.

const links = userLink.pick( 'name', 'email' ),
      { name, email } = links;

linkToObject.map( ( linkToItem, itemKey ) => any | void ) : any[]

Map and filter through array or object.

var list = stringArrayLink.map( ( itemLink, index ) => {
    if( itemLink.value ){ // Skip empty elements
        return (
            <div key={ index }>
                <Input valueLink={ itemLink } />
            </div>
        );
    }
});

Offhand boolean links

linkToArray.contains( element ) : Link

Creates the link to the presence of value in array.

Resulting link value is true whenever element is present in array, and false otherwise. Whenever resulting link is assigned with new value, it will flip element in the array.

Useful for the large checkbox groups.

const optionXBoolLink = arrayLink.contains( 'optionX' );

linkToAny.equals( whenTrue ) : Link

Create boolean link to value equality.

Resulting link value is true whenever parent link value equals to whenTrue, and false otherwise. When resulting link is assigned with true, it sets parent link value with whenTrue, and with null otherwise.

Useful for radio groups.

const optionXLink = stringLink.equals( 'optionX' );

linkToAny.enabled( defaultValue = '' ) : Link

Create boolean link which value is false when parent link is null (or undefined), and true otherwise. Whenever the enabled-link is set to true, it sets parent link to the defaultValue.

This type of links is used to support enabling/disabling of individual form controls with a dedicated checkbox. <Input> control and the rest of form controls must be modified to disable themselves when its valueLink.value === null.

const textLink = this.linkAt( 'text' );

return (
    <Checkbox checkedLink={ textLink.enabled() } />
    <Input valueLink={ textLink } /> 
);

Custom links

Link.value( value, nextValue => void ) : Link

Create custom link with the given value and update function.

It may be used for different scenarios. Good example is to use 'edit element' component for adding new element.

Imagine that we have a component <EditUser valueLink={ userLink } /> expecting the link to an object. When editing is finished, EditUser will update the given link with a new values.

Then, following custom link will allow you to add new user with the same form element.

<EditUser valueLink={ Link.value( {}, x => userArrayLink.push( x ) ) } />

Read more about links to objects updates in the next section.

link.onChange( callback : any => void ) : Link

Create the wrapper for existing link which will invoke callback whenever new value is set. Similar to:

Link.value( link.value, x => {
    callback( x );
    link.set( x );
});

link.pipe( transform : ( next, prev ) => any ) : Link

Create the wrapper for existing link which will invoke given transform function before new value is set. Returned value will be used as new link value, and if it's undefined update will be rejected. Similar to:

Link.value( link.value, x => {
    const y = callback( x, link.value );
    if( y !== undefined ){
        link.set( y );
    }
});

Usage example:

<Input valueLink={ strLink.pipe( x => x && x.toUpperCase() ) }/>

Note for TypeScript users

Link is the parametric type Link< T >, where T is the type of the enclosed value.

TypeScript properly infers type of the link and perform static checks failing on missing state members.

interface MyState {
    name : string
}
...
const nameLink = this.linkAt( 'name' ); // Link< string >
const missingLink = this.linkAt( 'age' ); // Compile-time error - no such a member in state.

Link updates

Simple value updates

link.set( x ) : void

link.requestChange( x ) : void

Set link to the given value.

<button onClick={ () => boolLink.set( !boolLink.value ) } />

link.update( prevValue => any ) : void

Update link value using the given value transform function.

<button onClick={ () => boolLink.update( x => !x ) } />

link.action( ( prevValue, event ) => any ) : ( event => void )

Create UI event handler which will transform the link.

link.action takes transform function, and produce a new function which takes single event argument. When it's called, event and link value are passes as transform parameters, and link will be updated with returned value.

This is particularly useful in (but not restricted to) UI event handlers.

// simple click event handler...
<button onClick={ boolLink.action( x => !x ) } />

// manual binding to input control:
const setValue = ( x, e ) => e.target.value;
...
<input  value={ link.value }
        onChange={ link.action( setValue ) } />

Link to objects and arrays updates

Plain objects and arrays are shallow copied by link.update() and within link.action() handlers, thus it's safe just to update the value in place.

linkToObject.update( clonedObject => Object ) : void

Update enclosed object or array.

linkToObject.action( ( clonedObject, event ) => Object ) : ( event => void )

Creates action to update enclosed object or array.

<button onClick={ () => objLink.update( obj => {
                                obj.a = 1;
                                return obj;
                            }) } />

linkToObject.removeAt( key ) : void

linkToObject.at( key ).remove() : void

Remove element with a given key from the enclosed object ar array.

Link to arrays updates

Link to arrays proxies some important Array methods.

linkToArray.splice( ... ) : void

linkToArray.push( ... ) : void

linkToArray.unshift( ... ) : void

Works in the same way and accepts the same parameters as corresponding Array method, but returns undefined and leads to the proper purely functional update of the parent object chain.

Links validation

It's highly recommended to read tutorial on validation with value links.

link.check( value => boolean, error = 'Invalid value' ) : Link

Evaluate given condition for the current link value, and assign given error object to the link.error when it fails. There are no restriction on the error object shape and type.

It's possible to assign default error message to the validator function. tags.jsx provides isRequired and isEmail generic validator functions as an examples. Excerpt from tags.jsx:

export const isRequired = x => x != null && x !== '';
isRequired.error = 'Required';

Checks can be chained. In this case, the first check which fails will leave its error in the link.

link.error : any | void

This link field may be analyzed by custom <Input /> control to indicate an error (see tags.jsx controls and supplied examples).

This mechanics can be used to add ad-hoc validation in render.

// Simple check
const numLink = List.state( this, 'num' )
                .check( x => x >= 0 && x <=5 );

console.log( numLink.error );

// Check with error message
const numLink = List.state( this, 'num' )
                .check( x => x >= 0 && x <=5, 'Number must be between 0 and 5' );

console.log( numLink.error );

// Chained checks
const numLink = List.state( this, 'num' )
                .check( x => x >= 0, 'Negative numbers are not allowed' )
                .check( x => x <= 5, 'Number should be not greater than 5' );

console.log( numLink.error );

Data binding examples

Here are the set of working examples for typical data binding use cases.

Also, there's working example of an application managing the users list.

Custom elements boilerplate which is used by both examples is another good example.

Text and number form fields

<Input type="text"/>, <TextArea />

tags.jsx contains wrappers for standard <input> and <textarea> tags, which can be directly bound to the string state elements.

These wrappers will add invalid class to enclosed HTML element, if an error is present in the bound link.

<Input type="text" valueLink={ link } />
<TextArea valueLink={ link } />

<NumberInput/>

There's also cross-browser implementation of numeric input tag. It has following differences compared to <Input>:

• Keyboard input which obviously leads to invalid values (e.g. letters) are rejected.
• Value is being always converted to valid number.
• There are integer and positive boolean props controlling input rejection. They can be combined.

<NumberInput> validates its value, and adds invalid class to enclosed input element if it's not a number.

<NumberInput valueLink={ link } />
<NumberInput valueLink={ link } integer={ true }/>
<NumberInput valueLink={ link } positive={ true }/>

Checkboxes

<Input type="checkbox" />

Wrapper for the standard <input>. Directly binds boolean value with checkedLink property.

<Input type="text" checkedLink={ booleanLink } />
<Input type="text" checkedLink={ arrayLink.contains( 'option' ) } />

<Checkbox/>

Internally, it's <div> element which toggles selected class on click. Thus, it can be easily styled.

By default, it has checkbox CSS class, which can be overridden by passing className prop.

It passes through anything else, including children.

<Checkbox checkedLink={ booleanLink } />
<Checkbox checkedLink={ arrayLink.contains( 'option' ) } />

Radio Groups and Select list

<Select/>

Wrapper for standard <select/>. Regular <option/> tags must be used. All props are passed through.

<Select valueLink={ linkToSelectedValue }>
    <option value="a">A</option>
    <option value="b">B</option>
</Select>

<Input type="radio"/>

Wrapper for the standard <input>. Directly binds boolean value with checkedLink property.

Can be directly bound to the state member using valueLink property.

<label>
    A:
    <Input type="radio" valueLink={ flagLink } value="a" />
</label>
<label>
    B:
    <Input type="radio" valueLink={ flagLink } value="b" />
</label>

<Radio/>

Internally, it's <div> element which always sets selected class on click. Thus, it can be easily styled.

By default, it has radio CSS class, which can be overridden by passing className prop. It passes through anything else, including children.

It must be used in conjunction with link.equals( 'value' ) method.

<label>
    A:
    <Radio checkedLink={ flagLink.equals( 'a' ) } />
</label>
<label>
    B:
    <Radio checkedLink={ flagLink.equals( 'b' ) } />
</label>