fix #121; add transition.selectChild[ren]

src/transition/index.js

@@ -43,6 +43,8 @@ Transition.prototype = transition.prototype = {
   constructor: Transition,
   select: transition_select,
   selectAll: transition_selectAll,
+  selectChild: selection_prototype.selectChild,
+  selectChildren: selection_prototype.selectChildren,
   filter: transition_filter,
   merge: transition_merge,
   selection: transition_selection,

test/transition/selectChild-test.js

@@ -0,0 +1,20 @@
+import assert from "assert";
+import {selectAll} from "d3-selection";
+import {transition} from "../../src/index.js";
+import it from "../jsdom.js";
+
+it("transition.selectChild(selector) selects the child matching the specified selector, then derives a transition", "<h1 id='one'><child/></h1><h1 id='two'><child/></h1>", () => {
+  const one = document.querySelector("#one");
+  const two = document.querySelector("#two");
+  const t1 = selectAll([one, two]).data([1, 2]).transition().delay(function(d) { return d * 10; });
+  const t2 = t1.selectChild("child");
+  assert.strictEqual(t2 instanceof transition, true);
+  assert.deepStrictEqual(t2._groups, [[one.firstChild, two.firstChild]]);
+  assert.strictEqual(t2._parents, t1._parents);
+  assert.strictEqual(t2._name, t1._name);
+  assert.strictEqual(t2._id, t1._id);
+  assert.strictEqual(one.firstChild.__data__, 1);
+  assert.strictEqual(two.firstChild.__data__, 2);
+  assert.strictEqual(one.firstChild.__transition[t1._id].delay, 10);
+  assert.strictEqual(two.firstChild.__transition[t1._id].delay, 20);
+});

test/transition/selectChildren-test.js

@@ -0,0 +1,20 @@
+import assert from "assert";
+import {selectAll} from "d3-selection";
+import {transition} from "../../src/index.js";
+import it from "../jsdom.js";
+
+it("transition.selectChildren(selector) selects the children matching the specified selector, then derives a transition", "<h1 id='one'><child/></h1><h1 id='two'><child/></h1>", () => {
+  const one = document.querySelector("#one");
+  const two = document.querySelector("#two");
+  const t1 = selectAll([one, two]).data([1, 2]).transition().delay(function(d) { return d * 10; });
+  const t2 = t1.selectChildren("child");
+  assert.strictEqual(t2 instanceof transition, true);
+  assert.deepStrictEqual(t2._groups.map(group => Array.from(group)), [[one.firstChild], [two.firstChild]]);
+  assert.deepStrictEqual(t2._parents, [one, two]);
+  assert.strictEqual(t2._name, t1._name);
+  assert.strictEqual(t2._id, t1._id);
+  assert.strictEqual("__data__" in one.firstChild, false);
+  assert.strictEqual("__data__" in two.firstChild, false);
+  assert.strictEqual(one.firstChild.__transition[t1._id].delay, 10);
+  assert.strictEqual(two.firstChild.__transition[t1._id].delay, 20);
+});