Preserve scriptable context (#7981)

* Preserve scriptable context
* CC, utilize `index` in tests
* Update example to utilize context

docs/docs/general/options.md

@@ -37,14 +37,52 @@ color: [
 ## Option Context
 
 The option context is used to give contextual information when resolving options and currently only applies to [scriptable options](#scriptable-options).
+The object is preserved, so it can be used to store and pass information between calls.
+
+There are multiple levels of context objects:
+
+- `chart`
+  - `dataset`
+    - `data`
+  - `scale`
+    - `tick`
+
+Each level inherits its parent(s) and any contextual information stored in the parent is available through the child.
 
 The context object contains the following properties:
 
+### chart
+
 - `chart`: the associated chart
-- `dataPoint`: the parsed data values for the given `dataIndex` and `datasetIndex`
-- `dataIndex`: index of the current data
+
+### dataset
+
+In addition to [chart](#chart)
+
+- `active`: true if element is active (hovered)
 - `dataset`: dataset at index `datasetIndex`
 - `datasetIndex`: index of the current dataset
-- `active`: true if element is active (hovered)
+- `index`: getter for `datasetIndex`
 
-**Important**: since the context can represent different types of entities (dataset, data, ticks, etc.), some properties may be `undefined` so be sure to test any context property before using it.
+### data
+
+In addition to [dataset](#dataset)
+
+- `active`: true if element is active (hovered)
+- `dataIndex`: index of the current data
+- `dataPoint`: the parsed data values for the given `dataIndex` and `datasetIndex`
+- `element`: the element (point, arc, bar, etc.) for this data
+- `index`: getter for `dataIndex`
+
+### scale
+
+In addition to [chart](#chart)
+
+- `scale`: the associated scale
+
+### tick
+
+In addition to [scale](#scale)
+
+- `tick`: the associated tick object
+- `index`: tick index

samples/animations/delay.html

@@ -63,7 +63,6 @@
 		};
 		window.onload = function() {
 			var ctx = document.getElementById('canvas').getContext('2d');
-			var started = {};
 			window.myBar = new Chart(ctx, {
 				type: 'bar',
 				data: barChartData,
@@ -77,9 +76,9 @@
 						var delay = 0;
 						var dsIndex = context.datasetIndex;
 						var index = context.dataIndex;
-						if (!started[index + dsIndex * 1000]) {
+						if (context.dataPoint && !context.delayed) {
 							delay = index * 300 + dsIndex * 100;
-							started[index + dsIndex * 1000] = true;
+							context.delayed = true;
 						}
 						return {
 							easing: 'linear',

src/core/core.controller.js

@@ -116,6 +116,7 @@ class Chart {
 		this._hiddenIndices = {};
 		this.attached = false;
 		this._animationsDisabled = undefined;
+		this.$context = undefined;
 
 		// Add the chart instance to the global namespace
 		Chart.instances[me.id] = me;
@@ -712,6 +713,14 @@ class Chart {
 		return meta;
 	}
 
+	getContext() {
+		return this.$context || (this.$context = Object.create(null, {
+			chart: {
+				value: this
+			}
+		}));
+	}
+
 	getVisibleDatasetCount() {
 		return this.getSortedVisibleDatasetMetas().length;
 	}

src/core/core.datasetController.js

@@ -148,6 +148,49 @@ function getFirstScaleId(chart, axis) {
 	return Object.keys(scales).filter(key => scales[key].axis === axis).shift();
 }
 
+function createDatasetContext(parent, index, dataset) {
+	return Object.create(parent, {
+		active: {
+			writable: true,
+			value: false
+		},
+		dataset: {
+			value: dataset
+		},
+		datasetIndex: {
+			value: index
+		},
+		index: {
+			get() {
+				return this.datasetIndex;
+			}
+		}
+	});
+}
+
+function createDataContext(parent, index, point, element) {
+	return Object.create(parent, {
+		active: {
+			writable: true,
+			value: false
+		},
+		dataIndex: {
+			value: index
+		},
+		dataPoint: {
+			value: point
+		},
+		element: {
+			value: element
+		},
+		index: {
+			get() {
+				return this.dataIndex;
+			}
+		}
+	});
+}
+
 const optionKeys = (optionNames) => isArray(optionNames) ? optionNames : Object.keys(optionNames);
 const optionKey = (key, active) => active ? 'hover' + _capitalize(key) : key;
 const isDirectUpdateMode = (mode) => mode === 'reset' || mode === 'none';
@@ -177,6 +220,7 @@ export default class DatasetController {
 		this._drawStart = undefined;
 		this._drawCount = undefined;
 		this.enableOptionSharing = false;
+		this.$context = undefined;
 
 		this.initialize();
 	}
@@ -491,6 +535,13 @@ export default class DatasetController {
 		return this._cachedMeta._parsed[index];
 	}
 
+	/**
+	 * @protected
+	 */
+	getDataElement(index) {
+		return this._cachedMeta.data[index];
+	}
+
 	/**
 	 * @protected
 	 */
@@ -698,14 +749,18 @@ export default class DatasetController {
 	 * @protected
 	 */
 	getContext(index, active) {
-		return {
-			chart: this.chart,
-			dataPoint: this.getParsed(index),
-			dataIndex: index,
-			dataset: this.getDataset(),
-			datasetIndex: this.index,
-			active
-		};
+		const me = this;
+		let context;
+		if (index >= 0 && index < me._cachedMeta.data.length) {
+			const element = me._cachedMeta.data[index];
+			context = element.$context ||
+				(element.$context = createDataContext(me.getContext(), index, me.getParsed(index), element));
+		} else {
+			context = me.$context || (me.$context = createDatasetContext(me.chart.getContext(), me.index, me.getDataset()));
+		}
+
+		context.active = !!active;
+		return context;
 	}
 
 	/**

src/core/core.scale.js

@@ -8,7 +8,7 @@ import Ticks from './core.ticks';
 
 /**
  * @typedef { import("./core.controller").default } Chart
- * @typedef {{value:any, label?:string, major?:boolean}} Tick
+ * @typedef {{value:any, label?:string, major?:boolean, $context?:any}} Tick
  */
 
 defaults.set('scale', {
@@ -269,6 +269,25 @@ function skip(ticks, newTicks, spacing, majorStart, majorEnd) {
 	}
 }
 
+function createScaleContext(parent, scale) {
+	return Object.create(parent, {
+		scale: {
+			value: scale
+		},
+	});
+}
+
+function createTickContext(parent, index, tick) {
+	return Object.create(parent, {
+		tick: {
+			value: tick
+		},
+		index: {
+			value: index
+		}
+	});
+}
+
 export default class Scale extends Element {
 
 	// eslint-disable-next-line max-statements
@@ -345,6 +364,7 @@ export default class Scale extends Element {
 		this._ticksLength = 0;
 		this._borderValue = 0;
 		this._cache = {};
+		this.$context = undefined;
 	}
 
 	/**
@@ -1043,13 +1063,16 @@ export default class Scale extends Element {
 	 * @protected
 	 */
 	getContext(index) {
-		const ticks = this.ticks || [];
-		return {
-			chart: this.chart,
-			scale: this,
-			tick: ticks[index],
-			index
-		};
+		const me = this;
+		const ticks = me.ticks || [];
+
+		if (index >= 0 && index < ticks.length) {
+			const tick = ticks[index];
+			return tick.$context ||
+				(tick.$context = createTickContext(me.getContext(), index, tick));
+		}
+		return me.$context ||
+			(me.$context = createScaleContext(me.chart.getContext(), me));
 	}
 
 	/**

test/fixtures/controller.line/backgroundColor/scriptable.js

@@ -8,7 +8,7 @@ module.exports = {
 					// option in dataset
 					data: [4, 5, 10, null, -10, -5],
 					backgroundColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#ff00ff';
@@ -26,7 +26,7 @@ module.exports = {
 			elements: {
 				line: {
 					backgroundColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#ff00ff';

test/fixtures/controller.line/borderColor/scriptable.js

@@ -8,7 +8,7 @@ module.exports = {
 					// option in dataset
 					data: [4, 5, 10, null, -10, -5],
 					borderColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#0000ff';
@@ -26,7 +26,7 @@ module.exports = {
 			elements: {
 				line: {
 					borderColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#0000ff';

test/fixtures/controller.line/borderWidth/scriptable.js

@@ -9,7 +9,7 @@ module.exports = {
 					data: [4, 5, 10, null, -10, -5],
 					borderColor: '#0000ff',
 					borderWidth: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index % 2 ? 10 : 20;
 					},
 					pointBorderColor: '#00ff00'
@@ -27,7 +27,7 @@ module.exports = {
 				line: {
 					borderColor: '#ff0000',
 					borderWidth: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index % 2 ? 10 : 20;
 					},
 					fill: false,

test/fixtures/controller.radar/backgroundColor/scriptable.js

@@ -8,7 +8,7 @@ module.exports = {
 					// option in dataset
 					data: [0, 5, 10, null, -10, -5],
 					backgroundColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#ff00ff';
@@ -26,7 +26,7 @@ module.exports = {
 			elements: {
 				line: {
 					backgroundColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#ff00ff';

test/fixtures/controller.radar/borderColor/scriptable.js

@@ -8,7 +8,7 @@ module.exports = {
 					// option in dataset
 					data: [0, 5, 10, null, -10, -5],
 					borderColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#0000ff';
@@ -26,7 +26,7 @@ module.exports = {
 			elements: {
 				line: {
 					borderColor: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index === 0 ? '#ff0000'
 							: index === 1 ? '#00ff00'
 							: '#0000ff';

test/fixtures/controller.radar/borderWidth/scriptable.js

@@ -9,7 +9,7 @@ module.exports = {
 					data: [0, 5, 10, null, -10, -5],
 					borderColor: '#0000ff',
 					borderWidth: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index % 2 ? 10 : 20;
 					},
 					pointBorderColor: '#00ff00'
@@ -27,7 +27,7 @@ module.exports = {
 				line: {
 					borderColor: '#ff0000',
 					borderWidth: function(ctx) {
-						var index = (ctx.dataIndex === undefined ? ctx.datasetIndex : ctx.dataIndex);
+						var index = ctx.index;
 						return index % 2 ? 10 : 20;
 					},
 					fill: false