don’t consider null comparable

src/ascending.js

@@ -1,3 +1,7 @@
 export default function(a, b) {
-  return a < b ? -1 : a > b ? 1 : a >= b ? 0 : NaN;
+  return a == null || b == null ? NaN
+    : a < b ? -1
+    : a > b ? 1
+    : a >= b ? 0
+    : NaN;
 }

src/descending.js

@@ -1,3 +1,7 @@
 export default function(a, b) {
-  return b < a ? -1 : b > a ? 1 : b >= a ? 0 : NaN;
+  return a == null || b == null ? NaN
+    : b < a ? -1
+    : b > a ? 1
+    : b >= a ? 0
+    : NaN;
 }

src/greatest.js

@@ -7,21 +7,19 @@ export default function greatest(values, compare = ascending) {
     let maxValue;
     for (const element of values) {
       const value = compare(element);
-      if (value != null && (defined
+      if (defined
           ? ascending(value, maxValue) > 0
-          : ascending(value, value) === 0
-        )) {
+          : ascending(value, value) === 0) {
         max = element;
         maxValue = value;
         defined = true;
       }
     }
   } else {
     for (const value of values) {
-      if (value != null && (defined
+      if (defined
           ? compare(value, max) > 0
-          : compare(value, value) === 0
-        )) {
+          : compare(value, value) === 0) {
         max = value;
         defined = true;
       }

src/greatestIndex.js

@@ -8,10 +8,9 @@ export default function greatestIndex(values, compare = ascending) {
   let index = -1;
   for (const value of values) {
     ++index;
-    if (value != null && (max < 0
+    if (max < 0
         ? compare(value, value) === 0
-        : compare(value, maxValue) > 0
-      )) {
+        : compare(value, maxValue) > 0) {
       maxValue = value;
       max = index;
     }

src/least.js

@@ -7,21 +7,19 @@ export default function least(values, compare = ascending) {
     let minValue;
     for (const element of values) {
       const value = compare(element);
-      if (value != null && (defined
+      if (defined
           ? ascending(value, minValue) < 0
-          : ascending(value, value) === 0
-        )) {
+          : ascending(value, value) === 0) {
         min = element;
         minValue = value;
         defined = true;
       }
     }
   } else {
     for (const value of values) {
-      if (value != null && (defined
+      if (defined
           ? compare(value, min) < 0
-          : compare(value, value) === 0
-        )) {
+          : compare(value, value) === 0) {
         min = value;
         defined = true;
       }

src/leastIndex.js

@@ -8,10 +8,9 @@ export default function leastIndex(values, compare = ascending) {
   let index = -1;
   for (const value of values) {
     ++index;
-    if (value != null && (min < 0
+    if (min < 0
         ? compare(value, value) === 0
-        : compare(value, minValue) < 0
-      )) {
+        : compare(value, minValue) < 0) {
       minValue = value;
       min = index;
     }

test/greatest-test.js

@@ -46,12 +46,12 @@ it("greatest(array) returns the first of equal values", () => {
   assert.deepStrictEqual(greatest([3, 2, 2, 1, 1, 0, 0, 0, 3, 0].map(box), ascendingValue), {value: 3, index: 0});
 });
 
-tape("greatest(array) ignores null and undefined", (test) => {
-  test.deepEqual(d3.greatest([null, -2, undefined]), -2);
+it("greatest(array) ignores null and undefined", () => {
+  assert.deepStrictEqual(greatest([null, -2, undefined]), -2);
 });
 
-tape("greatest(array, accessor) ignores null and undefined", (test) => {
-  test.deepEqual(d3.greatest([null, -2, undefined], d => d), -2);
+it("greatest(array, accessor) ignores null and undefined", () => {
+  assert.deepStrictEqual(greatest([null, -2, undefined], d => d), -2);
 });
 
 function box(value, index) {

test/greatestIndex-test.js

@@ -46,10 +46,10 @@ it("greatestIndex(array) returns the first of equal values", () => {
   assert.strictEqual(greatestIndex([-3, -2, -2, -1, -1, 0, 0, 0, -3, 0], descending), 0);
 });
 
-tape("greatestIndex(array) ignores null and undefined", (test) => {
-  test.deepEqual(d3.greatestIndex([null, -2, undefined]), 1);
+it("greatestIndex(array) ignores null and undefined", () => {
+  assert.deepStrictEqual(greatestIndex([null, -2, undefined]), 1);
 });
 
-tape("greatestIndex(array, accessor) ignores null and undefined", (test) => {
-  test.deepEqual(d3.greatestIndex([null, -2, undefined], d => d), 1);
+it("greatestIndex(array, accessor) ignores null and undefined", () => {
+  assert.deepStrictEqual(greatestIndex([null, -2, undefined], d => d), 1);
 });

test/least-test.js

@@ -46,12 +46,12 @@ it("least(array) returns the first of equal values", () => {
   assert.deepStrictEqual(least([3, 2, 2, 1, 1, 0, 0, 0, 3, 0].map(box), descendingValue), {value: 3, index: 0});
 });
 
-tape("least(array) ignores null and undefined", (test) => {
-  test.deepEqual(d3.least([null, 2, undefined]), 2);
+it("least(array) ignores null and undefined", () => {
+  assert.deepStrictEqual(least([null, 2, undefined]), 2);
 });
 
-tape("least(array, accessor) ignores null and undefined", (test) => {
-  test.deepEqual(d3.least([null, 2, undefined], d => d), 2);
+it("least(array, accessor) ignores null and undefined", () => {
+  assert.deepStrictEqual(least([null, 2, undefined], d => d), 2);
 });
 
 function box(value, index) {

test/leastIndex-test.js

@@ -46,10 +46,10 @@ it("leastIndex(array) returns the first of equal values", () => {
   assert.strictEqual(leastIndex([3, 2, 2, 1, 1, 0, 0, 0, 3, 0], descending), 0);
 });
 
-tape("leastIndex(array) ignores null and undefined", (test) => {
-  test.deepEqual(d3.leastIndex([null, 2, undefined]), 1);
+it("leastIndex(array) ignores null and undefined", () => {
+  assert.deepStrictEqual(leastIndex([null, 2, undefined]), 1);
 });
 
-tape("leastIndex(array, accessor) ignores null and undefined", (test) => {
-  test.deepEqual(d3.leastIndex([null, 2, undefined], d => d), 1);
+it("leastIndex(array, accessor) ignores null and undefined", () => {
+  assert.deepStrictEqual(leastIndex([null, 2, undefined], d => d), 1);
 });