fix: .instanceof to allow DOM interfaces in IE11

lib/chai/core/assertions.js

@@ -1601,28 +1601,25 @@ module.exports = function (chai, _) {
     var target = flag(this, 'object')
     var ssfi = flag(this, 'ssfi');
     var flagMsg = flag(this, 'message');
-    var validInstanceOfTarget = constructor === Object(constructor) && (
-        typeof constructor === 'function' ||
-        (typeof Symbol !== 'undefined' &&
-         typeof Symbol.hasInstance !== 'undefined' &&
-         Symbol.hasInstance in constructor)
-    );
 
-    if (!validInstanceOfTarget) {
-      flagMsg = flagMsg ? flagMsg + ': ' : '';
-      var constructorType = constructor === null ? 'null' : typeof constructor;
-      throw new AssertionError(
-        flagMsg + 'The instanceof assertion needs a constructor but ' + constructorType + ' was given.',
-        undefined,
-        ssfi
-      );
+    try {
+      var isInstanceOf = target instanceof constructor;
+    } catch (err) {
+      if (err instanceof TypeError) {
+        flagMsg = flagMsg ? flagMsg + ': ' : '';
+        throw new AssertionError(
+          flagMsg + 'The instanceof assertion needs a constructor but '
+            + _.type(constructor) + ' was given.',
+          undefined,
+          ssfi
+        );
+      }
+      throw err;
     }
 
-    var isInstanceOf = target instanceof constructor
-
     var name = _.getName(constructor);
     if (name === null) {
-        name = 'an unnamed constructor';
+      name = 'an unnamed constructor';
     }
 
     this.assert(

test/assert.js

@@ -145,6 +145,17 @@ describe('assert', function () {
     function Foo(){}
     assert.instanceOf(new Foo(), Foo);
 
+    // Normally, `instanceof` requires that the constructor be a function or an
+    // object with a callable `@@hasInstance`. But in some older browsers such
+    // as IE11, `instanceof` also accepts DOM-related interfaces such as
+    // `HTMLElement`, despite being non-callable objects in those browsers.
+    // See: https://github.com/chaijs/chai/issues/1000.
+    if (typeof document !== 'undefined' &&
+        typeof document.createElement !== 'undefined' &&
+        typeof HTMLElement !== 'undefined') {
+      assert.instanceOf(document.createElement('div'), HTMLElement);
+    }
+
     err(function(){
       assert.instanceOf(new Foo(), 1, 'blah');
     }, "blah: The instanceof assertion needs a constructor but number was given.");
@@ -155,7 +166,7 @@ describe('assert', function () {
 
     err(function(){
       assert.instanceOf(new Foo(), {});
-    }, "The instanceof assertion needs a constructor but object was given.");
+    }, "The instanceof assertion needs a constructor but Object was given.");
 
     err(function(){
       assert.instanceOf(new Foo(), true);
@@ -224,7 +235,7 @@ describe('assert', function () {
 
     err(function(){
       assert.notInstanceOf(new Foo(), {});
-    }, "The instanceof assertion needs a constructor but object was given.");
+    }, "The instanceof assertion needs a constructor but Object was given.");
 
     err(function(){
       assert.notInstanceOf(new Foo(), true);

test/expect.js

@@ -374,6 +374,17 @@ describe('expect', function () {
     function Foo(){}
     expect(new Foo()).to.be.an.instanceof(Foo);
 
+    // Normally, `instanceof` requires that the constructor be a function or an
+    // object with a callable `@@hasInstance`. But in some older browsers such
+    // as IE11, `instanceof` also accepts DOM-related interfaces such as
+    // `HTMLElement`, despite being non-callable objects in those browsers.
+    // See: https://github.com/chaijs/chai/issues/1000.
+    if (typeof document !== 'undefined' &&
+        typeof document.createElement !== 'undefined' &&
+        typeof HTMLElement !== 'undefined') {
+      expect(document.createElement('div')).to.be.an.instanceof(HTMLElement);
+    }
+
     err(function(){
       expect(new Foo()).to.an.instanceof(1, 'blah');
     }, "blah: The instanceof assertion needs a constructor but number was given.");
@@ -388,7 +399,7 @@ describe('expect', function () {
 
     err(function(){
       expect(new Foo()).to.an.instanceof({});
-    }, "The instanceof assertion needs a constructor but object was given.");
+    }, "The instanceof assertion needs a constructor but Object was given.");
 
     err(function(){
       expect(new Foo()).to.an.instanceof(true);

test/should.js

@@ -420,6 +420,17 @@ describe('should', function() {
     function Foo(){}
     new Foo().should.be.an.instanceof(Foo);
 
+    // Normally, `instanceof` requires that the constructor be a function or an
+    // object with a callable `@@hasInstance`. But in some older browsers such
+    // as IE11, `instanceof` also accepts DOM-related interfaces such as
+    // `HTMLElement`, despite being non-callable objects in those browsers.
+    // See: https://github.com/chaijs/chai/issues/1000.
+    if (typeof document !== 'undefined' &&
+        typeof document.createElement !== 'undefined' &&
+        typeof HTMLElement !== 'undefined') {
+      document.createElement('div').should.be.an.instanceof(HTMLElement);
+    }
+
     err(function(){
       new Foo().should.be.an.instanceof(1, 'blah');
     }, "blah: The instanceof assertion needs a constructor but number was given.");
@@ -430,7 +441,7 @@ describe('should', function() {
 
     err(function(){
       new Foo().should.be.an.instanceof({});
-    }, "The instanceof assertion needs a constructor but object was given.");
+    }, "The instanceof assertion needs a constructor but Object was given.");
 
     err(function(){
       new Foo().should.be.an.instanceof(true);