feat: add unregisterFilter method (#946)

* feat: add unregisterFilter method

* docs: show how to re-register built-in filters

---------

Co-authored-by: Yacov <yacov@noemail>

Author: YacovGold

docs/source/tutorials/register-filters-tags.md

@@ -62,7 +62,23 @@ See existing filter implementations here: <https://github.com/harttle/liquidjs/t
 
 ## Unregister Tags/Filters
 
-In some cases it's desirable to disable some tags/filters (see [#324](https://github.com/harttle/liquidjs/issues/324)). You'll need to register a dummy tag/filter that throws a corresponding Error.
+Filters can be unregistered by name:
+
+```javascript
+engine.unregisterFilter('plus')
+```
+
+With [`strictFilters`][strict-filters] enabled, using an unregistered filter will throw an error. Otherwise, the filter will be skipped.
+
+Built-in filters can be registered again using the exported `filters` object:
+
+```javascript
+import { filters } from 'liquidjs'
+
+engine.registerFilter('plus', filters.plus)
+```
+
+To disable a tag, or to make a disabled filter throw regardless of `strictFilters`, register a dummy implementation that throws a corresponding error (see [#324](https://github.com/harttle/liquidjs/issues/324)):
 
 ```javascript
 // disable a tag
@@ -81,3 +97,5 @@ function disabledFilter(name) {
 }
 engine.registerFilter('plus', disabledFilter('plus'));
 ```
+
+[strict-filters]: /tutorials/options.html#strict

src/liquid.ts

@@ -101,6 +101,9 @@ export class Liquid {
   public registerFilter (name: string, filter: FilterImplOptions) {
     this.filters[name] = filter
   }
+  public unregisterFilter (name: string) {
+    delete this.filters[name]
+  }
   public registerTag (name: string, tag: TagClass | TagImplOptions) {
     this.tags[name] = isFunction(tag) ? tag : createTagClass(tag)
   }

test/integration/liquid/register-filters.spec.ts

@@ -1,4 +1,4 @@
-import { Liquid } from '../../../src/liquid'
+import { Liquid, filters } from '../../../src'
 
 describe('liquid#registerFilter()', function () {
   let liquid: Liquid
@@ -67,3 +67,32 @@ describe('liquid#registerFilter()', function () {
     await expect(new Liquid({ strictFilters: true }).parseAndRender('{{ 1 | constructor }}')).rejects.toThrow('undefined filter')
   })
 })
+
+describe('liquid#unregisterFilter()', function () {
+  let liquid: Liquid
+  beforeEach(() => { liquid = new Liquid() })
+
+  it('should unregister a custom filter', async () => {
+    liquid.registerFilter('greet', value => `hello ${value}`)
+    liquid.unregisterFilter('greet')
+    const html = await liquid.parseAndRender('{{ "world" | greet }}')
+    return expect(html).toBe('world')
+  })
+
+  it('should unregister a built-in filter', () => {
+    liquid = new Liquid({ strictFilters: true })
+    liquid.unregisterFilter('upcase')
+    return expect(liquid.parseAndRender('{{ "foo" | upcase }}')).rejects.toThrow('undefined filter: upcase')
+  })
+
+  it('should support re-registering a built-in filter', async () => {
+    liquid.unregisterFilter('upcase')
+    liquid.registerFilter('upcase', filters.upcase)
+    const html = await liquid.parseAndRender('{{ "foo" | upcase }}')
+    return expect(html).toBe('FOO')
+  })
+
+  it('should not throw for an unknown filter', () => {
+    expect(() => liquid.unregisterFilter('unknown')).not.toThrow()
+  })
+})