lift side effect up to index.js

docs/features/transforms.md

@@ -181,7 +181,7 @@ The **transform** function is passed three arguments, *data*, *facets*, and *opt
 
 If the **transform** option is specified, it supersedes any basic transforms (*i.e.*, the **filter**, **sort** and **reverse** options are ignored). However, the **transform** option is rarely used directly; instead one of Plot’s built-in transforms are used, and these transforms automatically compose with the basic **filter**, **sort** and **reverse** transforms.
 
-While transform functions often produce new *data* or *facets*, they may return the passed-in *data* and *facets* as-is, and often have a side-effect of constructing derived channels. For example, the count of elements in a [groupX transform](../transforms/group.md) might be returned as a new *y* channel. In this case, the transform is typically expressed as an options transform: a function that takes a mark *options* object and returns a new, transformed options object, where the returned options object implements the **transform** option. Transform functions should not mutate the input *data* or *facets*. Likewise options transforms should not mutate the input *options* object.
+While transform functions often produce new *data* or *facets*, they may return the passed-in *data* and *facets* as-is, and often have a side effect of constructing derived channels. For example, the count of elements in a [groupX transform](../transforms/group.md) might be returned as a new *y* channel. In this case, the transform is typically expressed as an options transform: a function that takes a mark *options* object and returns a new, transformed options object, where the returned options object implements the **transform** option. Transform functions should not mutate the input *data* or *facets*. Likewise options transforms should not mutate the input *options* object.
 
 When implementing a custom transform for generic usage, keep in mind that it needs to be compatible with Plot’s [faceting system](./facets.md), which partitions the original dataset into discrete subsets.
 

package.json

@@ -44,7 +44,7 @@
     "@observablehq/plot": "./src/index.js"
   },
   "sideEffects": [
-    "./src/plot.js"
+    "./src/index.js"
   ],
   "devDependencies": {
     "@observablehq/runtime": "^5.7.3",

src/index.js

@@ -1,3 +1,11 @@
+import {Mark} from "./mark.js";
+import {plot} from "./plot.js";
+
+// Note: this side effect avoids a circular dependency.
+Mark.prototype.plot = function ({marks = [], ...options} = {}) {
+  return plot({...options, marks: [...marks, this]});
+};
+
 export {plot} from "./plot.js";
 export {Mark, marks} from "./mark.js";
 export {Area, area, areaX, areaY} from "./marks/area.js";

src/mark.js

@@ -131,7 +131,7 @@ export class Mark {
 }
 
 export function marks(...marks) {
-  marks.plot = Mark.prototype.plot; // Note: depends on side-effect in plot!
+  marks.plot = Mark.prototype.plot;
   return marks;
 }
 

src/plot.js

@@ -368,13 +368,6 @@ function createFigcaption(document, caption) {
   return e;
 }
 
-function plotThis({marks = [], ...options} = {}) {
-  return plot({...options, marks: [...marks, this]});
-}
-
-// Note: This side-effect avoids a circular dependency.
-Mark.prototype.plot = plotThis;
-
 function flatMarks(marks) {
   return marks
     .flat(Infinity)

src/transforms/basic.d.ts

@@ -10,7 +10,7 @@ import type {ScaleFunctions} from "../scales.js";
  * the data, *facets*, and the plot’s *options*. The transform function returns
  * new mark data and facets; the returned **data** defaults to the passed
  * *data*, and the returned **facets** defaults to the passed *facets*. The mark
- * is the *this* context. Transform functions can also trigger side-effects, say
+ * is the *this* context. Transform functions can also trigger side effects, say
  * to populate lazily-derived columns; see also Plot.column.
  */
 export type TransformFunction = (