Add type to context objects (#8007)

docs/docs/general/options.md

@@ -54,6 +54,7 @@ The context object contains the following properties:
 ### chart
 
 - `chart`: the associated chart
+- `type`: `'chart'`
 
 ### dataset
 
@@ -63,6 +64,7 @@ In addition to [chart](#chart)
 - `dataset`: dataset at index `datasetIndex`
 - `datasetIndex`: index of the current dataset
 - `index`: getter for `datasetIndex`
+- `type`: `'dataset'`
 
 ### data
 
@@ -73,12 +75,14 @@ In addition to [dataset](#dataset)
 - `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`
+- `type`: `'data'`
 
 ### scale
 
 In addition to [chart](#chart)
 
 - `scale`: the associated scale
+- `type`: `'scale'`
 
 ### tick
 
@@ -86,3 +90,4 @@ In addition to [scale](#scale)
 
 - `tick`: the associated tick object
 - `index`: tick index
+- `type`: `'tick'`

src/core/core.controller.js

@@ -735,6 +735,9 @@ class Chart {
 		return this.$context || (this.$context = Object.create(null, {
 			chart: {
 				value: this
+			},
+			type: {
+				value: 'chart'
 			}
 		}));
 	}

src/core/core.datasetController.js

@@ -164,6 +164,9 @@ function createDatasetContext(parent, index, dataset) {
 			get() {
 				return this.datasetIndex;
 			}
+		},
+		type: {
+			value: 'dataset'
 		}
 	});
 }
@@ -187,6 +190,9 @@ function createDataContext(parent, index, point, element) {
 			get() {
 				return this.dataIndex;
 			}
+		},
+		type: {
+			value: 'data',
 		}
 	});
 }

src/core/core.scale.js

@@ -274,6 +274,9 @@ function createScaleContext(parent, scale) {
 		scale: {
 			value: scale
 		},
+		type: {
+			value: 'scale'
+		}
 	});
 }
 
@@ -284,6 +287,9 @@ function createTickContext(parent, index, tick) {
 		},
 		index: {
 			value: index
+		},
+		type: {
+			value: 'tick'
 		}
 	});
 }