diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 7561783d1398b..eedcd456b84cd 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -222,8 +222,21 @@ namespace ts {
                 case SyntaxKind.ExportAssignment:
                     return (<ExportAssignment>node).isExportEquals ? "export=" : "default";
                 case SyntaxKind.BinaryExpression:
-                    // Binary expression case is for JS module 'module.exports = expr'
-                    return "export=";
+                    switch (getSpecialPropertyAssignmentKind(node)) {
+                        case SpecialPropertyAssignmentKind.ModuleExports:
+                            // module.exports = ...
+                            return "export=";
+                        case SpecialPropertyAssignmentKind.ExportsProperty:
+                        case SpecialPropertyAssignmentKind.ThisProperty:
+                            // exports.x = ... or this.y = ...
+                            return ((node as BinaryExpression).left as PropertyAccessExpression).name.text;
+                        case SpecialPropertyAssignmentKind.PrototypeProperty:
+                            // className.prototype.methodName = ...
+                            return (((node as BinaryExpression).left as PropertyAccessExpression).expression as PropertyAccessExpression).name.text;
+                    }
+                    Debug.fail("Unknown binary declaration kind");
+                    break;
+
                 case SyntaxKind.FunctionDeclaration:
                 case SyntaxKind.ClassDeclaration:
                     return node.flags & NodeFlags.Default ? "default" : undefined;
@@ -1166,11 +1179,25 @@ namespace ts {
                     return checkStrictModeIdentifier(<Identifier>node);
                 case SyntaxKind.BinaryExpression:
                     if (isInJavaScriptFile(node)) {
-                        if (isExportsPropertyAssignment(node)) {
-                            bindExportsPropertyAssignment(<BinaryExpression>node);
-                        }
-                        else if (isModuleExportsAssignment(node)) {
-                            bindModuleExportsAssignment(<BinaryExpression>node);
+                        const specialKind = getSpecialPropertyAssignmentKind(node);
+                        switch (specialKind) {
+                            case SpecialPropertyAssignmentKind.ExportsProperty:
+                                bindExportsPropertyAssignment(<BinaryExpression>node);
+                                break;
+                            case SpecialPropertyAssignmentKind.ModuleExports:
+                                bindModuleExportsAssignment(<BinaryExpression>node);
+                                break;
+                            case SpecialPropertyAssignmentKind.PrototypeProperty:
+                                bindPrototypePropertyAssignment(<BinaryExpression>node);
+                                break;
+                            case SpecialPropertyAssignmentKind.ThisProperty:
+                                bindThisPropertyAssignment(<BinaryExpression>node);
+                                break;
+                            case SpecialPropertyAssignmentKind.None:
+                                // Nothing to do
+                                break;
+                            default:
+                                Debug.fail("Unknown special property assignment kind");
                         }
                     }
                     return checkStrictModeBinaryExpression(<BinaryExpression>node);
@@ -1339,6 +1366,34 @@ namespace ts {
             bindExportAssignment(node);
         }
 
+        function bindThisPropertyAssignment(node: BinaryExpression) {
+            // Declare a 'member' in case it turns out the container was an ES5 class
+            if (container.kind === SyntaxKind.FunctionExpression || container.kind === SyntaxKind.FunctionDeclaration) {
+                container.symbol.members = container.symbol.members || {};
+                declareSymbol(container.symbol.members, container.symbol, node, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
+            }
+        }
+
+        function bindPrototypePropertyAssignment(node: BinaryExpression) {
+            // We saw a node of the form 'x.prototype.y = z'. Declare a 'member' y on x if x was a function.
+
+            // Look up the function in the local scope, since prototype assignments should
+            // follow the function declaration
+            const classId = <Identifier>(<PropertyAccessExpression>(<PropertyAccessExpression>node.left).expression).expression;
+            const funcSymbol = container.locals[classId.text];
+            if (!funcSymbol || !(funcSymbol.flags & SymbolFlags.Function)) {
+                return;
+            }
+
+            // Set up the members collection if it doesn't exist already
+            if (!funcSymbol.members) {
+                funcSymbol.members = {};
+            }
+
+            // Declare the method/property
+            declareSymbol(funcSymbol.members, funcSymbol, <PropertyAccessExpression>node.left, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
+        }
+
         function bindCallExpression(node: CallExpression) {
             // We're only inspecting call expressions to detect CommonJS modules, so we can skip
             // this check if we've already seen the module indicator
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6d69c45dbce98..5bfa474422446 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2664,9 +2664,13 @@ namespace ts {
                 if (declaration.kind === SyntaxKind.BinaryExpression) {
                     return links.type = checkExpression((<BinaryExpression>declaration).right);
                 }
-                // Handle exports.p = expr
                 if (declaration.kind === SyntaxKind.PropertyAccessExpression) {
-                    return checkExpressionCached((<BinaryExpression>declaration.parent).right);
+                    // Declarations only exist for property access expressions for certain
+                    // special assignment kinds
+                    if (declaration.parent.kind === SyntaxKind.BinaryExpression) {
+                        // Handle exports.p = expr or this.p = expr or className.prototype.method = expr
+                        return links.type = checkExpressionCached((<BinaryExpression>declaration.parent).right);
+                    }
                 }
                 // Handle variable, parameter or property
                 if (!pushTypeResolution(symbol, TypeSystemPropertyName.Type)) {
@@ -6888,6 +6892,23 @@ namespace ts {
                 const symbol = getSymbolOfNode(container.parent);
                 return container.flags & NodeFlags.Static ? getTypeOfSymbol(symbol) : (<InterfaceType>getDeclaredTypeOfSymbol(symbol)).thisType;
             }
+
+            // If this is a function in a JS file, it might be a class method. Check if it's the RHS
+            // of a x.prototype.y = function [name]() { .... }
+            if (isInJavaScriptFile(node) && container.kind === SyntaxKind.FunctionExpression) {
+                if (getSpecialPropertyAssignmentKind(container.parent) === SpecialPropertyAssignmentKind.PrototypeProperty) {
+                    // Get the 'x' of 'x.prototype.y = f' (here, 'f' is 'container')
+                    const className = (((container.parent as BinaryExpression)   // x.protoype.y = f
+                                        .left as PropertyAccessExpression)       // x.prototype.y
+                                        .expression as PropertyAccessExpression) // x.prototype
+                                        .expression;                             // x
+                    const classSymbol = checkExpression(className).symbol;
+                    if (classSymbol && classSymbol.members && (classSymbol.flags & SymbolFlags.Function)) {
+                        return getInferredClassType(classSymbol);
+                    }
+                }
+            }
+
             return anyType;
         }
 
@@ -9609,6 +9630,14 @@ namespace ts {
             return links.resolvedSignature;
         }
 
+        function getInferredClassType(symbol: Symbol) {
+            const links = getSymbolLinks(symbol);
+            if (!links.inferredClassType) {
+                links.inferredClassType = createAnonymousType(undefined, symbol.members, emptyArray, emptyArray, /*stringIndexType*/ undefined, /*numberIndexType*/ undefined);
+            }
+            return links.inferredClassType;
+        }
+
         /**
          * Syntactically and semantically checks a call or new expression.
          * @param node The call/new expression to be checked.
@@ -9630,8 +9659,14 @@ namespace ts {
                     declaration.kind !== SyntaxKind.ConstructSignature &&
                     declaration.kind !== SyntaxKind.ConstructorType) {
 
-                    // When resolved signature is a call signature (and not a construct signature) the result type is any
-                    if (compilerOptions.noImplicitAny) {
+                    // When resolved signature is a call signature (and not a construct signature) the result type is any, unless
+                    // the declaring function had members created through 'x.prototype.y = expr' or 'this.y = expr' psuedodeclarations
+                    // in a JS file
+                    const funcSymbol = checkExpression(node.expression).symbol;
+                    if (funcSymbol && funcSymbol.members && (funcSymbol.flags & SymbolFlags.Function)) {
+                        return getInferredClassType(funcSymbol);
+                    }
+                    else if (compilerOptions.noImplicitAny) {
                         error(node, Diagnostics.new_expression_whose_target_lacks_a_construct_signature_implicitly_has_an_any_type);
                     }
                     return anyType;
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 9411437c9815f..2e557ad09a460 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -1997,6 +1997,7 @@ namespace ts {
         type?: Type;                        // Type of value symbol
         declaredType?: Type;                // Type of class, interface, enum, type alias, or type parameter
         typeParameters?: TypeParameter[];   // Type parameters of type alias (undefined if non-generic)
+        inferredClassType?: Type;           // Type of an inferred ES5 class
         instantiations?: Map<Type>;         // Instantiations of generic type alias (undefined if non-generic)
         mapper?: TypeMapper;                // Type mapper for instantiation alias
         referenced?: boolean;               // True if alias symbol has been referenced as a value
@@ -2290,6 +2291,19 @@ namespace ts {
         // It is optional because in contextual signature instantiation, nothing fails
     }
 
+    /* @internal */
+    export const enum SpecialPropertyAssignmentKind {
+        None,
+        /// exports.name = expr
+        ExportsProperty,
+        /// module.exports = expr
+        ModuleExports,
+        /// className.prototype.name = expr
+        PrototypeProperty,
+        /// this.name = expr
+        ThisProperty
+    }
+
     export interface DiagnosticMessage {
         key: string;
         category: DiagnosticCategory;
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 95bf4ff7fa32b..6730f38a84896 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1063,33 +1063,40 @@ namespace ts {
                 (<CallExpression>expression).arguments[0].kind === SyntaxKind.StringLiteral;
     }
 
-    /**
-     * Returns true if the node is an assignment to a property on the identifier 'exports'.
-     * This function does not test if the node is in a JavaScript file or not.
-    */
-    export function isExportsPropertyAssignment(expression: Node): boolean {
-        // of the form 'exports.name = expr' where 'name' and 'expr' are arbitrary
-        return isInJavaScriptFile(expression) &&
-            (expression.kind === SyntaxKind.BinaryExpression) &&
-            ((<BinaryExpression>expression).operatorToken.kind === SyntaxKind.EqualsToken) &&
-            ((<BinaryExpression>expression).left.kind === SyntaxKind.PropertyAccessExpression) &&
-            ((<PropertyAccessExpression>(<BinaryExpression>expression).left).expression.kind === SyntaxKind.Identifier) &&
-            ((<Identifier>((<PropertyAccessExpression>(<BinaryExpression>expression).left).expression)).text === "exports");
-    }
+    /// Given a BinaryExpression, returns SpecialPropertyAssignmentKind for the various kinds of property
+    /// assignments we treat as special in the binder
+    export function getSpecialPropertyAssignmentKind(expression: Node): SpecialPropertyAssignmentKind {
+        if (expression.kind !== SyntaxKind.BinaryExpression) {
+            return SpecialPropertyAssignmentKind.None;
+        }
+        const expr = <BinaryExpression>expression;
+        if (expr.operatorToken.kind !== SyntaxKind.EqualsToken || expr.left.kind !== SyntaxKind.PropertyAccessExpression) {
+            return SpecialPropertyAssignmentKind.None;
+        }
+        const lhs = <PropertyAccessExpression>expr.left;
+        if (lhs.expression.kind === SyntaxKind.Identifier) {
+            const lhsId = <Identifier>lhs.expression;
+            if (lhsId.text === "exports") {
+                // exports.name = expr
+                return SpecialPropertyAssignmentKind.ExportsProperty;
+            }
+            else if (lhsId.text === "module" && lhs.name.text === "exports") {
+                // module.exports = expr
+                return SpecialPropertyAssignmentKind.ModuleExports;
+            }
+        }
+        else if (lhs.expression.kind === SyntaxKind.ThisKeyword) {
+            return SpecialPropertyAssignmentKind.ThisProperty;
+        }
+        else if (lhs.expression.kind === SyntaxKind.PropertyAccessExpression) {
+            // chained dot, e.g. x.y.z = expr; this var is the 'x.y' part
+            const innerPropertyAccess = <PropertyAccessExpression>lhs.expression;
+            if (innerPropertyAccess.expression.kind === SyntaxKind.Identifier && innerPropertyAccess.name.text === "prototype") {
+                return SpecialPropertyAssignmentKind.PrototypeProperty;
+            }
+        }
 
-    /**
-     * Returns true if the node is an assignment to the property access expression 'module.exports'.
-     * This function does not test if the node is in a JavaScript file or not.
-    */
-    export function isModuleExportsAssignment(expression: Node): boolean {
-        // of the form 'module.exports = expr' where 'expr' is arbitrary
-        return isInJavaScriptFile(expression) &&
-            (expression.kind === SyntaxKind.BinaryExpression) &&
-            ((<BinaryExpression>expression).operatorToken.kind === SyntaxKind.EqualsToken) &&
-            ((<BinaryExpression>expression).left.kind === SyntaxKind.PropertyAccessExpression) &&
-            ((<PropertyAccessExpression>(<BinaryExpression>expression).left).expression.kind === SyntaxKind.Identifier) &&
-            ((<Identifier>((<PropertyAccessExpression>(<BinaryExpression>expression).left).expression)).text === "module") &&
-            ((<PropertyAccessExpression>(<BinaryExpression>expression).left).name.text === "exports");
+        return SpecialPropertyAssignmentKind.None;
     }
 
     export function getExternalModuleName(node: Node): Expression {
diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index 9d7293457816b..24f3319285b22 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -1162,7 +1162,7 @@ namespace FourSlash {
 
         public printCurrentQuickInfo() {
             const quickInfo = this.languageService.getQuickInfoAtPosition(this.activeFile.fileName, this.currentCaretPosition);
-            Harness.IO.log(JSON.stringify(quickInfo));
+            Harness.IO.log("Quick Info: " + quickInfo.displayParts.map(part => part.text).join(""));
         }
 
         public printErrorList() {
@@ -1204,12 +1204,26 @@ namespace FourSlash {
 
         public printMemberListMembers() {
             const members = this.getMemberListAtCaret();
-            Harness.IO.log(JSON.stringify(members));
+            this.printMembersOrCompletions(members);
         }
 
         public printCompletionListMembers() {
             const completions = this.getCompletionListAtCaret();
-            Harness.IO.log(JSON.stringify(completions));
+            this.printMembersOrCompletions(completions);
+        }
+
+        private printMembersOrCompletions(info: ts.CompletionInfo) {
+            function pad(s: string, length: number) {
+                return s + new Array(length - s.length + 1).join(" ");
+            }
+            function max<T>(arr: T[], selector: (x: T) => number): number {
+                return arr.reduce((prev, x) => Math.max(prev, selector(x)), 0);
+            }
+            const longestNameLength = max(info.entries, m => m.name.length);
+            const longestKindLength = max(info.entries, m => m.kind.length);
+            info.entries.sort((m, n) => m.sortText > n.sortText ? 1 : m.sortText < n.sortText ? -1 : m.name > n.name ? 1 : m.name < n.name ? -1 : 0);
+            const membersString = info.entries.map(m => `${pad(m.name, longestNameLength)} ${pad(m.kind, longestKindLength)} ${m.kindModifiers}`).join("\n");
+            Harness.IO.log(membersString);
         }
 
         public printReferences() {
@@ -3287,4 +3301,4 @@ namespace FourSlashInterface {
             };
         }
     }
-}
+}
diff --git a/tests/cases/fourslash/javaScriptPrototype1.ts b/tests/cases/fourslash/javaScriptPrototype1.ts
new file mode 100644
index 0000000000000..c9c454cfb2c7d
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptPrototype1.ts
@@ -0,0 +1,46 @@
+///<reference path="fourslash.ts" />
+
+// Assignments to the 'prototype' property of a function create a class
+
+// @allowNonTsExtensions: true
+// @Filename: myMod.js
+//// function myCtor(x) {
+//// }
+//// myCtor.prototype.foo = function() { return 32 };
+//// myCtor.prototype.bar = function() { return '' };
+//// 
+//// var m = new myCtor(10);
+//// m/*1*/
+//// var a = m.foo;
+//// a/*2*/
+//// var b = a();
+//// b/*3*/
+//// var c = m.bar();
+//// c/*4*/
+
+
+// Members of the class instance
+goTo.marker('1');
+edit.insert('.');
+verify.memberListContains('foo', undefined, undefined, 'property');
+verify.memberListContains('bar', undefined, undefined, 'property');
+edit.backspace();
+
+// Members of a class method (1)
+goTo.marker('2');
+edit.insert('.');
+verify.memberListContains('length', undefined, undefined, 'property');
+edit.backspace();
+
+// Members of the invocation of a class method (1)
+goTo.marker('3');
+edit.insert('.');
+verify.memberListContains('toFixed', undefined, undefined, 'method');
+verify.not.memberListContains('substr', undefined, undefined, 'method');
+edit.backspace();
+
+// Members of the invocation of a class method (2)
+goTo.marker('4');
+edit.insert('.');
+verify.memberListContains('substr', undefined, undefined, 'method');
+verify.not.memberListContains('toFixed', undefined, undefined, 'method');
diff --git a/tests/cases/fourslash/javaScriptPrototype2.ts b/tests/cases/fourslash/javaScriptPrototype2.ts
new file mode 100644
index 0000000000000..ab6afff3d2ce7
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptPrototype2.ts
@@ -0,0 +1,36 @@
+///<reference path="fourslash.ts" />
+
+// Assignments to 'this' in the constructorish body create
+// properties with those names
+
+// @allowNonTsExtensions: true
+// @Filename: myMod.js
+//// function myCtor(x) {
+////     this.qua = 10;
+//// }
+//// myCtor.prototype.foo = function() { return 32 };
+//// myCtor.prototype.bar = function() { return '' };
+//// 
+//// var m = new myCtor(10);
+//// m/*1*/
+//// var x = m.qua;
+//// x/*2*/
+//// myCtor/*3*/
+
+// Verify the instance property exists
+goTo.marker('1');
+edit.insert('.');
+verify.completionListContains('qua', undefined, undefined, 'property');
+edit.backspace();
+
+// Verify the type of the instance property
+goTo.marker('2');
+edit.insert('.');
+verify.completionListContains('toFixed', undefined, undefined, 'method');
+
+goTo.marker('3');
+edit.insert('.');
+// Make sure symbols don't leak out into the constructor
+verify.completionListContains('qua', undefined, undefined, 'warning');
+verify.completionListContains('foo', undefined, undefined, 'warning');
+verify.completionListContains('bar', undefined, undefined, 'warning');
diff --git a/tests/cases/fourslash/javaScriptPrototype3.ts b/tests/cases/fourslash/javaScriptPrototype3.ts
new file mode 100644
index 0000000000000..7b3f63eca57f1
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptPrototype3.ts
@@ -0,0 +1,20 @@
+///<reference path="fourslash.ts" />
+
+// Inside an inferred method body, the type of 'this' is the class type
+
+// @allowNonTsExtensions: true
+// @Filename: myMod.js
+//// function myCtor(x) {
+////     this.qua = 10;
+//// }
+//// myCtor.prototype.foo = function() { return this/**/; };
+//// myCtor.prototype.bar = function() { return '' };
+//// 
+
+goTo.marker();
+edit.insert('.');
+
+// Check members of the function
+verify.completionListContains('foo', undefined, undefined, 'property');
+verify.completionListContains('bar', undefined, undefined, 'property');
+verify.completionListContains('qua', undefined, undefined, 'property');
diff --git a/tests/cases/fourslash/javaScriptPrototype4.ts b/tests/cases/fourslash/javaScriptPrototype4.ts
new file mode 100644
index 0000000000000..81cb5fe378424
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptPrototype4.ts
@@ -0,0 +1,21 @@
+///<reference path="fourslash.ts" />
+
+// Check for any odd symbol leakage
+
+// @allowNonTsExtensions: true
+// @Filename: myMod.js
+//// function myCtor(x) {
+////     this.qua = 10;
+//// }
+//// myCtor.prototype.foo = function() { return 32 };
+//// myCtor.prototype.bar = function() { return '' };
+//// 
+//// myCtor/*1*/
+
+goTo.marker('1');
+edit.insert('.');
+
+// Check members of the function
+verify.completionListContains('foo', undefined, undefined, 'warning');
+verify.completionListContains('bar', undefined, undefined, 'warning');
+verify.completionListContains('qua', undefined, undefined, 'warning');
diff --git a/tests/cases/fourslash/javaScriptPrototype5.ts b/tests/cases/fourslash/javaScriptPrototype5.ts
new file mode 100644
index 0000000000000..a0125e4751213
--- /dev/null
+++ b/tests/cases/fourslash/javaScriptPrototype5.ts
@@ -0,0 +1,19 @@
+///<reference path="fourslash.ts" />
+
+// No prototype assignments are needed to enable class inference
+
+// @allowNonTsExtensions: true
+// @Filename: myMod.js
+//// function myCtor() {
+////     this.foo = 'hello';
+////     this.bar = 10;
+//// }
+//// let x = new myCtor();
+//// x/**/
+
+goTo.marker();
+edit.insert('.');
+
+// Check members of the function
+verify.completionListContains('foo', undefined, undefined, 'property');
+verify.completionListContains('bar', undefined, undefined, 'property');