Angular JSON Schema Form

A JSON Schema Form builder for Angular 4 and 5, similar to, and mostly API compatible with,

• JSON Schema Form's Angular Schema Form for AngularJS (examples)
• Mozilla's React JSON Schema Form for React (examples), and
• Joshfire's JSON Form for jQuery (examples)

Note: This is currently a personal proof-of-concept project, and is not affiliated with any of the organizations listed above. (Though they are all awesome, and totally worth checking out.)

Breaking change in version 0.7.0-alpha.2 and above

You must now import both JsonSchemaFormModule and a framework module. (Don't worry, it's easy.) For full details, see 'To install from NPM and use in your own project', below.

Check out the live demo and play with the examples

Check out some examples here.

This example playground features over 70 different JSON Schemas for you to try (including all examples used by each of the three libraries listed above), and the ability to quickly view any example formatted with Bootstrap 3, Bootstrap 4, or without any formatting.

Installation

To install from GitHub

To install the library and the example playground from GitHub, clone https://github.com/catull/ngx-json-schema.git with your favorite git program. Or, assuming you have git and Node/NPM installed, enter the following in your terminal:

git clone https://github.com/catull/ngx-json-schema.git ngx-json-schema
cd ngx-json-schema
npm install
npm start

This should start a server with the example playground, which you can view in your browser at http://localhost:4200

All the source code is in the /src folder. Inside that folder, you will find the following sub-folders:

• lib/src - Angular JSON Schema Form main library
• lib/src/framework-library - framework library
• lib/src/widget-library - widget library
• lib/src/shared - various utilities and helper functions
• demo - the demonstration playground example application
• demo/assets/example-schemas - JSON Schema examples used in the playground

If you want detailed documentation describing the individual functions used in this library, run npm run docs to generate TypeDoc documentation, and then look in the generated /docs/api folder. (Angular JSON Schema Form is still a work in progress, so right now this documentation varies from highly detailed to completely missing.)

To install from NPM and use in your own project

If, after playing with the examples, you decide this library is functional enough to use in your own project, you can install it from NPM using either NPM or Yarn. To install with NPM, run the following from your terminal:

npm install ngx-json-schema

Then import JsonSchemaFormModule in your main application module, like this:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import {
  JsonSchemaFormModule, Bootstrap3DesignFrameworkModule
} from 'ngx-json-schema';

import { AppComponent } from './app.component';

@NgModule({
  declarations: [ AppComponent ],
  imports: [
    BrowserModule,
    Bootstrap3DesignFrameworkModule,
    JsonSchemaFormModule.forRoot(Bootstrap3DesignFrameworkModule)
  ],
  providers: [],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

Note that you have to import both the main JsonSchemaFormModule and a separate framework module (in this example, Bootstrap3DesignFrameworkModule).

The framework module is listed in your imports section twice, once by itself (to load the framework's components) and again in the JsonSchemaFormModule.forRoot() function (to load the framework's service and tell Angular JSON Schema Form to use it).

Four framework modules are currently included:

• Bootstrap3FrameworkModule — Bootstrap 3
• Bootstrap4FrameworkModule — Bootstrap 4
• NoFrameworkModule — plain HTML (for testing)

It is also possible to load multiple frameworks and switch between them at runtime, like the example playground on GitHub. But most typical sites will just load one framework.

Seed Application Examples

For complete examples of how to install and configure Angular JSON Schema Form to work with each included display framework, check out the following seed applications:

• Angular JSON Schema Form Bootstrap 3 Seed App
• Angular JSON Schema Form Bootstrap 4 Seed App

Additional notes for Angular CLI

Make sure you are running a recent version of Angular CLI.

Very old versions of Angular CLI (e.g. 1.0.1) may fail with the error Critical dependency: the request of a dependency is an expression while trying to compile ajv (Another JSON Schema Validator). But this error has been fixed in newer versions. So if you receive that error, upgrade your Angular CLI.

Additional notes for SystemJS

If you use SystemJS, you will also need to make the following changes to your systemjs.config.js file. (If you're using a recent version of Angular CLI, or you don't have a systemjs.config.js file in your project, that means you're not using SystemJS, and you can safely ignore this section.)

Add these lines to the 'map' section of systemjs.config.js:

'ngx-json-schema': 'npm:ngx-json-schema/bundles/ngx-json-schema.umd.js',
'ajv':                       'npm:ajv/dist/ajv.min.js',
'lodash':                    'npm:lodash/lodash.min.js'

(Note: These instructions have not been tested recently. If you use SystemJS and have problems, please post a bug report on GitHub.)

Using Angular JSON Schema Form

Basic use

For basic use, after loading JsonSchemaFormModule as described above, to display a form in your Angular component, simply add the following to your component's template:

<json-schema-form
  loadExternalAssets="true"
  [schema]="yourJsonSchema"
  (onSubmit)="yourOnSubmitFn($event)">
</json-schema-form>

Where schema is a valid JSON schema object, and onSubmit calls a function to process the submitted JSON form data. If you don't already have your own schemas, you can find a bunch of samples to test with in the src/demo/assets/example-schemas folder, as described above.

Setting loadExternalAssets="true" will automatically load any additional assets needed by the display framework. It is useful when you are trying out this library, but production sites should instead load all required assets separately. For full details see 'Changing or adding frameworks', below.

Data-only mode

Angular JSON Schema Form can also create a form entirely from a JSON object—with no schema—like so:

<json-schema-form
  loadExternalAssets="true"
  [(ngModel)]="exampleJsonObject">
</json-schema-form>

exampleJsonObject = {
  "first_name": "Jane", "last_name": "Doe", "age": 25, "is_company": false,
  "address": {
    "street_1": "123 Main St.", "street_2": null,
    "city": "Las Vegas", "state": "NV", "zip_code": "89123"
  },
  "phone_numbers": [
    { "number": "702-123-4567", "type": "cell" },
    { "number": "702-987-6543", "type": "work" }
  ], "notes": ""
};

In this mode, Angular JSON Schema Form automatically generates a schema from your data. The generated schema is relatively simple, compared to what you could create on your own. However, as the above example shows, it does detect and enforce string, number, and boolean values (nulls are also assumed to be strings), and automatically allows array elements to be added, removed, and reordered.

After displaying a form in this mode, you can also use the formSchema and formLayout outputs (described in 'Debugging inputs and outputs', below), to return the generated schema and layout, which will give you a head start on writing your own schemas and layouts by showing you examples created from your own data.

Also, notice that the 'ngModel' input supports Angular's 2-way data binding, just like other form controls, which is why it is not always necessary to use an onSubmit function.

Advanced use

Additional inputs an outputs

For more control over your form, you may provide these additional inputs:

• layout array with a custom form layout (see Angular Schema Form's form definitions for information about how to construct a form layout)
• data object to populate the form with default or previously submitted values
• options object to set any global options for the form
• widgets object to add custom widgets
• language string to set the error message language (currently supports 'en' and 'fr')
• framework string or object to set which framework to use

For framework, you can pass in your own custom framework object, or, if you've loaded multiple frameworks, you can specify the name of the framework you want to use. To switch between the included frameworks, use 'material-design', 'bootstrap-3', 'bootstrap-4', and 'no-framework'.

If you want more detailed output, you may provide additional functions for onChanges to read the values in real time as the form is being filled out, and you may implement your own custom validation indicators from the boolean isValid or the detailed validationErrors outputs.

Here is an example:

<json-schema-form
  [schema]="yourJsonSchema"
  [layout]="yourJsonFormLayout"
  [(data)]="yourData"
  [options]="yourFormOptions"
  [widgets]="yourCustomWidgets"
  language="fr"
  framework="material-design"
  loadExternalAssets="true"
  (onChanges)="yourOnChangesFn($event)"
  (onSubmit)="yourOnSubmitFn($event)"
  (isValid)="yourIsValidFn($event)"
  (validationErrors)="yourValidationErrorsFn($event)">
</json-schema-form>

Note: If you prefer brackets around all your attributes, the following is functionally equivalent:

<json-schema-form
[schema]="yourJsonSchema"
[layout]="yourJsonFormLayout"
[(data)]="yourData"
[options]="yourFormOptions"
[widgets]="yourCustomWidgets"
[language]="'fr'"
[framework]="'material-design'"
[loadExternalAssets]="true"
(onChanges)="yourOnChangesFn($event)"
(onSubmit)="yourOnSubmitFn($event)"
(isValid)="yourIsValidFn($event)"
(validationErrors)="yourValidationErrorsFn($event)">
</json-schema-form>

If you use this syntax, make sure to include the nested quotes ("' and '") around the language and framework names. (If you leave out the inner quotes, Angular will read them as a variable names, rather than strings, which will cause errors. All un-bracketed attributes, however, are automatically read as strings, so they don't need inner quotes.)

Single-input mode

You may also combine all your inputs into one compound object and include it as a form input, like so:

let yourCompoundInputObject = {
  schema:    { ... },  // REQUIRED
  layout:    [ ... ],  // optional
  data:      { ... },  // optional
  options:   { ... },  // optional
  widgets:   { ... },  // optional
  language:   '...' ,  // optional
  framework:  '...'    // (or { ... }) optional
}

<json-schema-form
  [form]="yourCompoundInputObject"
  (onSubmit)="yourOnSubmitFn($event)">
</json-schema-form>

You can also mix these two styles depending on your needs. In the example playground, all examples use the combined form input for schema, layout, and data, which enables each example to control those three inputs, but the playground uses separate inputs for language and framework, enabling it to change those settings independent of the example.

Combining inputs is useful if you have many unique forms and store each form's data and schema together. If you have one form (or many identical forms), it will likely be more useful to use separate inputs for your data and schema. Though even in that case, if you use a custom layout, you could store your schema and layout together and use one input for both.

Compatibility modes

If you have previously used another JSON form creation library—Angular Schema Form (for AngularJS), React JSON Schema Form, or JSON Form (for jQuery)—in order to make the transition easier, Angular JSON Schema Form will recognize the input names and custom input objects used by those libraries. It should automatically work with JSON Schemas in version 6, version 4, version 3, or the truncated version 3 format supported by JSON Form. So the following will all work:

Angular Schema Form (AngularJS) compatibility:

<json-schema-form
  [schema]="yourJsonSchema"
  [form]="yourAngularSchemaFormLayout"
  [(model)]="yourData">
</json-schema-form>

React JSON Schema Form compatibility:

<json-schema-form
  [schema]="yourJsonSchema"
  [UISchema]="yourReactJsonSchemaFormUISchema"
  [(formData)]="yourData">
</json-schema-form>

JSON Form (jQuery) compatibility:

<json-schema-form
  [form]="{
    schema: yourJsonSchema,
    form: yourJsonFormLayout,
    customFormItems: yourJsonFormCustomFormItems,
    value: yourData
  }">
</json-schema-form>

Note: 2-way data binding will work with any dedicated data input, including 'data', 'model', 'ngModel', or 'formData'. However, 2-way binding will not work with the combined 'form' input.

Debugging inputs and outputs

Finally, Angular JSON Schema Form includes some additional inputs and outputs for debugging:

• debug input — Activates debugging mode.
• loadExternalAssets input — Causes external JavaScript and CSS needed by the selected framework to be automatically loaded from a CDN (this is not 100% reliable, so while this can be helpful during development and testing, it is not recommended for production)—Note: If you are using this mode and get a console error saying an external asset has not loaded (such as jQuery, required for Bootstrap 3) simply reloading your web browser will usually fix it.
• formSchema and formLayout outputs — Returns the final schema and layout used to create the form (which will either show how your original input schema and layout were modified, if you provided inputs, or show you the automatically generated ones, if you didn't).

<json-schema-form
  [schema]="yourJsonSchema"
  [debug]="true"
  loadExternalAssets="true"
  (formSchema)="showFormSchemaFn($event)"
  (formLayout)="showFormLayoutFn($event)">
</json-schema-form>

Customizing

In addition to a large number of user-settable options, Angular JSON Schema Form also has the ability to load custom form control widgets and layout frameworks. All forms are constructed from these basic components. The default widget library includes all standard HTML 5 form controls, as well as several common layout patterns, such as multiple checkboxes and tab sets. The default framework library includes templates to style forms using Bootstrap 3, or Bootstrap 4 (or plain HTML with no formatting, which is not useful in production, but can be helpful for development and debugging).

User settings

(TODO: List all available user settings, and configuration options for each.)

Creating custom input validation error messages

You can easily add your own custom input validation error messages, either for individual control widgets, or for your entire form.

Setting error messages for individual controls or the entire form

To set messages for individual form controls, add them to that control's node in the form layout, like this:

let yourFormLayout = [
  { key: 'name',
    title: 'Enter your name',
    validationMessages: {
      // Put your error messages for the 'name' field here
    }
  },
  { type: 'submit', title: 'Submit' }
]

To set messages for the entire form, add them to the form options, inside the defautWidgetOptions validationMessages object, like this:

let yourFormOptions = {
  defautWidgetOptions: {
    validationMessages: {
      // Put your error messages for the entire form here
    }
  }
}

How to format error messages

The validationMessages object—in either a layout node or the form options—contains the names of each error message you want to set as keys, and the corresponding messages as values. Messages may be in any of the following formats:

• String: A plain text message, which is always the same.
• String template: A text message that includes Angular template-style {{variables}}, which will be be replaced with values from the returned error object.
• Function: A JavaScript function which accepts the error object as input, and returns a string error message.

Here are examples of all three error message types:

validationMessages: {

  // String error message
  required: 'This field is required.',

  // String template error message
  // - minimumLength variable will be replaced
  minLength: 'Must be at least {{minimumLength}} characters long.',

  // Function error message
  // - example error object:   { multipleOfValue: 0.01, currentValue: 3.456 }
  // - resulting error message: 'Must have 2 or fewer decimal places.'
  multipleOf: function(error) {
    if ((1 / error.multipleOfValue) % 10 === 0) {
      const decimals = Math.log10(1 / error.multipleOfValue);
      return `Must have ${decimals} or fewer decimal places.`;
    } else {
      return `Must be a multiple of ${error.multipleOfValue}.`;
    }
  }
}

(Note: These examples are from the default set of built-in error messages, which includes messages for all JSON Schema errors except type, const, enum, and dependencies.)

Available input validation errors and object values

Here is a list of all the built-in JSON Schema errors, which data type each error is available for, and the values in their returned error objects:

Error name | Data type | Returned error object values -----------------|-----------|----------------------------------------- required | any | (none) type | any | requiredType, currentValue const | any | requiredValue, currentValue enum | any | allowedValues, currentValue minLength | string | minimumLength, currentLength maxLength | string | maximumLength, currentLength pattern | string | requiredPattern, currentValue format | string | requiredFormat, currentValue minimum | number | minimumValue, currentValue exclusiveMinimum | number | exclusiveMinimumValue, currentValue maximum | number | maximumValue, currentValue exclusiveMaximum | number | exclusiveMaximumValue, currentValue multipleOf | number | multipleOfValue, currentValue minProperties | object | minimumProperties, currentProperties maxProperties | object | maximumProperties, currentProperties dependencies * | object | (varies, based on dependencies schema) minItems | array | minimumItems, currentItems maxItems | array | maximumItems, currentItems uniqueItems | array | duplicateItems contains * | array | requiredItem

• Note: The contains and dependencies validators are still in development, and do not yet work correctly.

Changing or adding widgets

To add a new widget or override an existing widget, either add an object containing your new widgets to the widgets input of the <json-schema-form> tag, or load the WidgetLibraryService and call registerWidget(widgetType, widgetComponent), with a string type name and an Angular component to be used whenever a form needs that widget type.

Example:

import { YourInputWidgetComponent } from './your-input-widget.component';
import { YourCustomWidgetComponent } from './your-custom-widget.component';
...
let yourNewWidgets = {
  input: YourInputWidgetComponent,          // Replace existing 'input' widget
  custom-control: YourCustomWidgetComponent // Add new 'custom-control' widget
}

...and...

<json-schema-form
  [schema]="yourJsonSchema"
  [widgets]="yourNewWidgets">
</json-schema-form>

...or...

import { WidgetLibraryService } from 'ngx-json-schema';
...
constructor(private widgetLibrary: WidgetLibraryService) { }
...
// Replace existing 'input' widget:
widgetLibrary.registerWidget('input', YourInputWidgetComponent);
// Add new 'custom-control' widget:
widgetLibrary.registerWidget('custom-control', YourCustomWidgetComponent);

To see many examples of widgets, explore the source code, or call getAllWidgets() from the WidgetLibraryService to see all widgets currently available in the library. All default widget components are in the /src/lib/src/widget-library folder, and all custom Bootstrap 3 widget components are in the /src/lib/src/framework-library/bootstrap-3-framework folder. (The Bootstrap 3 and Bootstrap 4 frameworks just reformat the default widgets, and so do not include any custom widgets of their own.)

Changing or adding frameworks

To change the active framework, either use the framework input of the <json-schema-form> tag, or load the FrameworkLibraryService and call setFramework(yourCustomFramework), with either the name of an available framework ('bootstrap-3', 'bootstrap-4', 'material-design', or 'no-framework'), or with your own custom framework object, like so:

import { YourFrameworkComponent } from './your-framework.component';
import { YourWidgetComponent } from './your-widget.component';
...
let yourCustomFramework = {
  framework: YourFrameworkComponent,                                // required
  widgets:     { 'your-widget-name': YourWidgetComponent,   ... },  // optional
  stylesheets: [ '//url-to-framework-external-style-sheet', ... ],  // optional
  scripts:     [ '//url-to-framework-external-script',      ... ]   // optional
}

...and...

<json-schema-form
  [schema]="yourJsonSchema"
  [framework]="yourCustomFramework">
</json-schema-form>

...or...

import { FrameworkLibraryService } from 'ngx-json-schema';
...
constructor(private frameworkLibrary: FrameworkLibraryService) { }
...
frameworkLibrary.setFramework(yourCustomFramework);

The value of the required framework key is an Angular component which will be called to format each widget before it is displayed. The optional widgets object contains any custom widgets, which will override or supplement the built-in widgets. And the optional stylesheets and scripts arrays contain URLs to any additional external style sheets or JavaScript libraries required by the framework. These are the external stylesheets and scripts that will be loaded if the "loadExternalAssets" option is set to "true".

Loading external assets required by a framework

Most Web layout framework libraries (including Bootstrap) need additional external JavaScript and/or CSS assets loaded in order to work properly. The best practice is to load these assets separately in your site, before calling Angular JSON Schema Form. (For the included libraries, follow these links for more information about how to do this: Bootstrap.)

Alternately, during development, you may find it helpful to let Angular JSON Schema Form load these resources for you (as wed did in the 'Basic use' example, above), which you can do in several ways:

• Call setFramework with a second parameter of true (e.g. setFramework('material-design', true)), or
• Add loadExternalAssets: true to your options object, or
• Add loadExternalAssets="true" to your <json-schema-form> tag, as shown above

Finally, if you want to see what scripts a particular framework will automatically load, after setting that framework you can call getFrameworkStylesheets() or getFrameworkScritps() from the FrameworkLibraryService to return the built-in arrays of URLs.

However, if you are creating a production site you should load these assets separately, and make sure to remove all references to loadExternalAssets to prevent the assets from being loaded twice.

Two approaches to writing your own frameworks

The two built-in frameworks (in the /src/lib/src/framework-library folder) demonstrate different strategies for how frameworks can style form elements. The Bootstrap 3 and Bootstrap 4 frameworks are very lightweight and include no additional widgets (though they do load some external stylesheets and scripts). They work entirely by adding styles to the default widgets.

Contributions and future development

If you find this library useful, I'd love to hear from you. If you have any trouble with it or would like to request a feature, please post an issue on GitHub.

If you're a programmer and would like a fun intermediate-level Angular project to hack on, clone the library and take a look at the source code. I wrote this library both because I needed an Angular JSON Schema Form builder, and also as a way to sharpen my Angular skills. This project is just complex enough to be challenging and fun, but not so difficult as to be overwhelming. One thing I particularly like is that each example in the demo playground is like a little puzzle which provides immediate feedback—as soon as it works perfectly, you know you've solved it.

I've also tried to split things into small modules as much as possible, so even though some code is still a bit messy, most individual parts should be straightforward to work with. (A lot of the code is well commented, though some isn't—but I'm working to fix that. If you run into anything you don't understand, please ask.) If you make improvements, please submit a pull request to share what you've done.

This library is mostly functional (I'm already using it in another large site, where it works well), but it still has many small bugs to fix and enhancements that could be made. Here's a random list of some stuff I know needs to be added or improved:

• TDD tests—The single biggest flaw in this library is that each change or improvement has the potential to break something else (which has already happened several times). Integrating automated tests into the build process would fix that.

• More frameworks—Not everyone uses Bootstrap 3, or Bootstrap 4, so it would be great to create framework plug-ins for Foundation 6, Semantic UI, or other web design frameworks.

• More widgets—There are lots of great form controls available, such as the Pikaday calendar, Spectrum color picker, and ACE code editor, which just need small custom wrappers to convert them into Angular JSON Schema Form plug-ins. In addition, there are a few additional features of HTML, JSON Schema, which could be fixed by adding new widgets:

  • A file widget—To support uploading files, this widget would display an HTML file input, and then include the uploaded file in the form's output data, as an ArrayBuffer or DataURL.

  • A oneOf widget—To support schemas using oneOf or anyOf, this widget would enable a user to choose an option from a select list, which would then replace another control on the form.

  • An addAdditionalProperties widget—To support schemas using additionalProperties or patternProperties, this widget would enable users to enter a name to add a new property to an object, and would then add a new control to the form for setting that property's value (similar to the existing add-reference widget).

If you like this library, need help, or want to contribute, let me know. I'm busy, so it sometimes takes me a long time to respond, but I will eventually get back to you. :-)

Thanks! I hope you enjoy using this library as much as I enjoyed writing it.

License

MIT