fix order of arguments validation in String.prototype.{ startsWith, endsWith } polyfills

Author: zloirock

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Fixed iterator closing in `Set.prototype.{ isDisjointFrom, isSupersetOf }` polyfill
 - Fixed (updated following the final spec) one more case `Set.prototype.difference` polyfill with updating `this`
 - Fixed `DataView.prototype.setFloat16` polyfill in (0, 1) range
+- Fixed order of arguments validation in `String.prototype.{ startsWith, endsWith }` polyfills
 - Fixed named backreferences in `RegExp` NCG polyfill
 - Fixed some cases of `RegExp` NCG polyfill in combination with other types of groups
 - Fixed some cases of `RegExp` NCG polyfill in combination with `dotAll`

packages/core-js/modules/es.string.ends-with.js

@@ -25,10 +25,10 @@ $({ target: 'String', proto: true, forced: !MDN_POLYFILL_BUG && !CORRECT_IS_REGE
   endsWith: function endsWith(searchString /* , endPosition = @length */) {
     var that = toString(requireObjectCoercible(this));
     notARegExp(searchString);
+    var search = toString(searchString);
     var endPosition = arguments.length > 1 ? arguments[1] : undefined;
     var len = that.length;
     var end = endPosition === undefined ? len : min(toLength(endPosition), len);
-    var search = toString(searchString);
     return slice(that, end - search.length, end) === search;
   }
 });

packages/core-js/modules/es.string.starts-with.js

@@ -25,8 +25,8 @@ $({ target: 'String', proto: true, forced: !MDN_POLYFILL_BUG && !CORRECT_IS_REGE
   startsWith: function startsWith(searchString /* , position = 0 */) {
     var that = toString(requireObjectCoercible(this));
     notARegExp(searchString);
-    var index = toLength(min(arguments.length > 1 ? arguments[1] : undefined, that.length));
     var search = toString(searchString);
+    var index = toLength(min(arguments.length > 1 ? arguments[1] : undefined, that.length));
     return stringSlice(that, index, index + search.length) === search;
   }
 });

tests/unit-global/es.string.ends-with.js

@@ -42,4 +42,11 @@ QUnit.test('String#endsWith', assert => {
   assert.notThrows(() => '[object Object]'.endsWith(object));
   object[Symbol.match] = true;
   assert.throws(() => '[object Object]'.endsWith(object), TypeError);
+  // side-effect ordering: ToString(searchString) should happen before ToIntegerOrInfinity(endPosition)
+  const order = [];
+  'abc'.endsWith(
+    { toString() { order.push('search'); return 'c'; } },
+    { valueOf() { order.push('pos'); return 3; } },
+  );
+  assert.deepEqual(order, ['search', 'pos'], 'ToString(searchString) before ToIntegerOrInfinity(endPosition)');
 });

tests/unit-global/es.string.starts-with.js

@@ -41,4 +41,11 @@ QUnit.test('String#startsWith', assert => {
   assert.notThrows(() => '[object Object]'.startsWith(object));
   object[Symbol.match] = true;
   assert.throws(() => '[object Object]'.startsWith(object), TypeError);
+  // side-effect ordering: ToString(searchString) should happen before ToIntegerOrInfinity(position)
+  const order = [];
+  'abc'.startsWith(
+    { toString() { order.push('search'); return 'a'; } },
+    { valueOf() { order.push('pos'); return 0; } },
+  );
+  assert.deepEqual(order, ['search', 'pos'], 'ToString(searchString) before ToIntegerOrInfinity(position)');
 });

tests/unit-pure/es.string.ends-with.js

@@ -37,4 +37,12 @@ QUnit.test('String#endsWith', assert => {
   assert.notThrows(() => endsWith('[object Object]', object));
   object[Symbol.match] = true;
   assert.throws(() => endsWith('[object Object]', object), TypeError);
+  // side-effect ordering: ToString(searchString) should happen before ToIntegerOrInfinity(endPosition)
+  const order = [];
+  endsWith(
+    'abc',
+    { toString() { order.push('search'); return 'c'; } },
+    { valueOf() { order.push('pos'); return 3; } },
+  );
+  assert.deepEqual(order, ['search', 'pos'], 'ToString(searchString) before ToIntegerOrInfinity(endPosition)');
 });

tests/unit-pure/es.string.starts-with.js

@@ -37,4 +37,12 @@ QUnit.test('String#startsWith', assert => {
   assert.notThrows(() => startsWith('[object Object]', object));
   object[Symbol.match] = true;
   assert.throws(() => startsWith('[object Object]', object), TypeError);
+  // side-effect ordering: ToString(searchString) should happen before ToIntegerOrInfinity(position)
+  const order = [];
+  startsWith(
+    'abc',
+    { toString() { order.push('search'); return 'a'; } },
+    { valueOf() { order.push('pos'); return 0; } },
+  );
+  assert.deepEqual(order, ['search', 'pos'], 'ToString(searchString) before ToIntegerOrInfinity(position)');
 });