add setSeed to randomization

packages/jspsych/src/modules/randomization.ts

@@ -1,4 +1,20 @@
 import rw from "random-words";
+import seedrandom from "seedrandom";
+
+/**
+ * Uses the `seedrandom` package to replace Math.random() with a seedable PRNG.
+ *
+ * @param seed An optional seed. If none is given, a random seed will be generated.
+ * @returns The seed value.
+ */
+export function setSeed(seed?) {
+  if (!seed) {
+    const prng = seedrandom();
+    seed = prng.int32();
+  }
+  seedrandom(seed, { global: true });
+  return seed;
+}
 
 export function repeat(array, repetitions, unpack = false) {
   const arr_isArray = Array.isArray(array);

packages/jspsych/tests/randomization/randomziation.test.ts

@@ -3,6 +3,7 @@ import {
   randomID,
   randomInt,
   repeat,
+  setSeed,
   shuffle,
   shuffleAlternateGroups,
   shuffleNoRepeats,
@@ -165,3 +166,20 @@ describe("randomInt", () => {
     }).toThrowError();
   });
 });
+
+describe("setSeed", () => {
+  test("Replaces Math.random() with seedable RNG", () => {
+    setSeed(12603);
+
+    const r1_1 = Math.random();
+    const r1_2 = Math.random();
+
+    setSeed(12603);
+
+    const r2_1 = Math.random();
+    const r2_2 = Math.random();
+
+    expect(r1_1).toEqual(r2_1);
+    expect(r1_2).toEqual(r2_2);
+  });
+});

packages/jspsych/tests/randomization/setseed.test.ts

@@ -0,0 +1,93 @@
+// this file is to test that jsPsych.randomization.setSeed works in context
+
+import htmlKeyboardResponse from "@jspsych/plugin-html-keyboard-response";
+import { pressKey, startTimeline } from "@jspsych/test-utils";
+
+import { initJsPsych } from "../../src";
+
+describe("setSeed generates predictable randomization", () => {
+  test("timeline variable randomization is preserved", async () => {
+    const jsPsych = initJsPsych();
+
+    const seed = jsPsych.randomization.setSeed();
+
+    const { getData } = await startTimeline(
+      [
+        {
+          timeline: [
+            {
+              type: htmlKeyboardResponse,
+              stimulus: "this is html",
+              data: {
+                i: jsPsych.timelineVariable("i"),
+              },
+            },
+          ],
+          timeline_variables: [
+            { i: 0 },
+            { i: 1 },
+            { i: 2 },
+            { i: 3 },
+            { i: 4 },
+            { i: 5 },
+            { i: 6 },
+            { i: 7 },
+            { i: 8 },
+          ],
+          randomize_order: true,
+        },
+      ],
+      jsPsych
+    );
+
+    for (let i = 0; i < 9; i++) {
+      pressKey(" ");
+    }
+
+    const data_run_1 = getData().readOnly();
+
+    const jsPsych_run2 = initJsPsych();
+
+    jsPsych_run2.randomization.setSeed(seed);
+
+    const { getData: getData2 } = await startTimeline(
+      [
+        {
+          timeline: [
+            {
+              type: htmlKeyboardResponse,
+              stimulus: "this is html",
+              data: {
+                i: jsPsych_run2.timelineVariable("i"),
+              },
+            },
+          ],
+          timeline_variables: [
+            { i: 0 },
+            { i: 1 },
+            { i: 2 },
+            { i: 3 },
+            { i: 4 },
+            { i: 5 },
+            { i: 6 },
+            { i: 7 },
+            { i: 8 },
+          ],
+          randomize_order: true,
+        },
+      ],
+      jsPsych_run2
+    );
+
+    for (let i = 0; i < 9; i++) {
+      pressKey(" ");
+    }
+
+    const data_run_2 = getData2().readOnly();
+
+    console.log(data_run_1.values());
+    console.log(data_run_2.values());
+
+    expect(data_run_1.select("i").values).toEqual(data_run_2.select("i").values);
+  });
+});