Add defined and loaded elements to annotation context (chartjs#869)

* Add loaded elements to annotation context

* added types and doc

* read only elements

* added test cases modifying the annotations

docs/guide/options.md

@@ -116,6 +116,7 @@ In addition to [chart](#chart)
 
 * `id`: the annotation id
 * `element`: the annotation element
+* `elements`: the array which contains the already created annotation elements.
 * `type`: `'annotation'`
 
 The [annotation](#annotation) option context is passed to scriptable options in all other cases, except when resolving `id`, `type` or adjusting scale ranges. The same values resolved in `afterDataLimits` with [chart](#chart) context are again evaluated in `afterUpdate` with [annotation](#annotation) context.

src/elements.js

@@ -52,7 +52,7 @@ export function updateElements(chart, state, options, mode) {
   for (let i = 0; i < annotations.length; i++) {
     const annotationOptions = annotations[i];
     const element = getOrCreateElement(elements, i, annotationOptions.type);
-    const resolver = annotationOptions.setContext(getContext(chart, element, annotationOptions));
+    const resolver = annotationOptions.setContext(getContext(chart, element, elements, annotationOptions));
     const properties = element.resolveElementProperties(chart, resolver);
 
     properties.skip = toSkip(properties);
@@ -142,9 +142,12 @@ function resolveObj(resolver, defs) {
   return result;
 }
 
-function getContext(chart, element, annotation) {
+function getContext(chart, element, elements, annotation) {
   return element.$context || (element.$context = Object.assign(Object.create(chart.getContext()), {
     element,
+    get elements() {
+      return elements.filter((el) => el && el.options);
+    },
     id: annotation.id,
     type: 'annotation'
   }));

test/specs/annotation.spec.js

@@ -211,4 +211,94 @@ describe('Annotation plugin', function() {
       expect(element.options.drawTime).toBe(chart.options.plugins.annotation.annotations.label.drawTime);
     });
   });
+
+  describe('context', function() {
+    it('should contain the loaded elements', function() {
+      const counts = [];
+      const annotations = [];
+      for (let i = 0; i < 5; i++) {
+        annotations.push({
+          type: 'label',
+          content: 'test',
+          display(context) {
+            expect(context.elements.length).toBe(i);
+            counts.push(i);
+          }
+        });
+      }
+      acquireChart({
+        type: 'line',
+        options: {
+          plugins: {
+            annotation: {
+              annotations
+            }
+          }
+        }
+      });
+      expect(counts).toEqual([0, 1, 2, 3, 4]);
+    });
+    it('should contain the loaded elements after update', function() {
+      const counts = [];
+      const annotations = [];
+      for (let i = 0; i < 5; i++) {
+        annotations.push({
+          type: 'label',
+          content: 'test',
+          display(context) {
+            expect(context.elements.length).toBe(i);
+            counts.push(i);
+          }
+        });
+      }
+      const chart = acquireChart({
+        type: 'line',
+        options: {
+          plugins: {
+            annotation: {
+              annotations
+            }
+          }
+        }
+      });
+      counts.splice(0, counts.length);
+      chart.update();
+      expect(counts).toEqual([0, 1, 2, 3, 4]);
+    });
+
+    it('should contain the loaded elements after reducing annotations and chart update', function() {
+      const counts = [];
+      const annotations = [];
+      for (let i = 0; i < 5; i++) {
+        annotations.push({
+          type: 'label',
+          content: 'test',
+          display(context) {
+            const check = context.chart.options.plugins.annotation.annotations.length < 5;
+            if (check) {
+              expect(context.elements.length).toBe(i - 2);
+              counts.push(i);
+            }
+          }
+        });
+      }
+      const chart = acquireChart({
+        type: 'line',
+        options: {
+          plugins: {
+            annotation: {
+              annotations
+            }
+          }
+        }
+      });
+      counts.splice(0, counts.length);
+      chart.update();
+      counts.splice(0, counts.length);
+      chart.options.plugins.annotation.annotations = annotations.slice(2);
+      chart.update();
+      expect(counts).toEqual([2, 3, 4]);
+    });
+
+  });
 });

types/events.d.ts

@@ -4,6 +4,7 @@ import { AnnotationElement } from './element';
 export interface EventContext {
   chart: Chart,
   element: AnnotationElement,
+  elements: AnnotationElement[],
   id: string,
   type: string
 }
@@ -15,6 +16,7 @@ export interface EventContext {
 export interface PartialEventContext {
   chart: Chart,
   element?: Partial<AnnotationElement>,
+  elements?: AnnotationElement[],
   id?: string,
   type?: string
 }