Add custom elements and attributes to compiler schema

Question

There are some custom elements and attributes in component template (in this example they are used by third-party non-Angular code):

<foo></foo>
<div data-bar="{{ bar }}"></div>

They cause a compiler error:

Template parse errors:
'foo' is not a known element:
1. If 'foo' is an Angular component, then verify that it is part of this module.
2. If 'foo' is a Web Component then add "CUSTOM_ELEMENTS_SCHEMA" to the '@NgModule.schemas' of this component to suppress this message. ("
    [ERROR ->]<foo></foo>
    <div data-bar="{{ bar }}"></div>
  "): App@1:4
Can't bind to 'bar' since it isn't a known property of 'div'. ("
    <foo></foo>
    <div [ERROR ->]data-bar="{{ bar }}"></div>
  ")
...

How can foo element and data-bar attribute be added to compiler schema?

NO_ERRORS_SCHEMA is not an option because it is not desirable for other unknown elements and attributes to be whitelisted.

Answer 1

You can try to override DomElementSchemaRegistry like this:

import { DomElementSchemaRegistry, ElementSchemaRegistry } from '@angular/compiler'
import { SchemaMetadata } from '@angular/core';

const MY_DOM_ELEMENT_SCHEMA = [
  'foo'
];

const MY_CUSTOM_PROPERTIES_SCHEMA = {
  'div': {
    'bar': 'string'
  }
};

export class CustomDomElementSchemaRegistry extends DomElementSchemaRegistry {
  constructor() {
    super();
  }

  hasElement(tagName: string, schemaMetas: SchemaMetadata[]): boolean {
    return MY_DOM_ELEMENT_SCHEMA.indexOf(tagName) > -1 || 
         super.hasElement(tagName, schemaMetas);
  }

  hasProperty(tagName: string, propName: string, schemaMetas: SchemaMetadata[]): boolean {
    const elementProperties = MY_CUSTOM_PROPERTIES_SCHEMA[tagName.toLowerCase()];
    return (elementProperties && elementProperties[propName]) || 
        super.hasProperty(tagName, propName, schemaMetas);
  }
}

platformBrowserDynamic().bootstrapModule(AppModule, {
  providers: [{ provide: ElementSchemaRegistry, useClass: CustomDomElementSchemaRegistry }]
});

Plunker Example

Answer 2

Looking good, but notice in you Plunker Example, the div in the markup is as below:

data-bar="{{ bar }}"

bar being = "test" is outputting on the dom just as:

<div></div>

and not

<div data-bar="test"></div>

If you want the attribute rendered - say for polymer components you can use the following.

[attr.data-bar]="bar" in the markup

Answer 3

Injecting CustomDomElementSchemaRegistry works now-a-days a little-bit differently:

JIT compiler

The injector has changed since the previous answer, so the type signature changed a very little. From version 5 StaticInjector needs the deps array with useClass (Angular 8.2)

platformBrowserDynamic().bootstrapModule(AppModule, 
 {
   providers: [
    { 
       provide: ElementSchemaRegistry, 
       useClass: CustomDomElementSchemaRegistry, 
       deps: [] 
    }
   ]
 }
);

AOT compiler

We can NOT use the injector for ahead of time compilation, but there is a possiblity to "monkey-patch" the class DomElementSchemaRegistry before it is instantiated by the compiler, for a detailed description check it here:

https://medium.com/angular-in-depth/angular-elementschemaregistry-for-dummies-83d54cd31478