diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 35140855d81..616bf5e70c0 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1016,8 +1016,8 @@ namespace ts {
             }
         }
 
-        const literalFiles = reduceOwnProperties(literalFileMap, addFileToOutput, []);
-        const wildcardFiles = reduceOwnProperties(wildcardFileMap, addFileToOutput, []);
+        const literalFiles = reduceProperties(literalFileMap, addFileToOutput, []);
+        const wildcardFiles = reduceProperties(wildcardFileMap, addFileToOutput, []);
         wildcardFiles.sort(host.useCaseSensitiveFileNames ? compareStrings : compareStringsCaseInsensitive);
         return {
             fileNames: literalFiles.concat(wildcardFiles),
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index d10d76b3492..40341929c02 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -30,8 +30,10 @@ namespace ts {
         map["__"] = undefined;
         delete map["__"];
 
-        if (template) {
-            copyOwnProperties(template, map);
+        // Copies keys/values from template. Note that for..in will not throw if
+        // template is undefined, and instead will just exit the loop.
+        for (const key in template) if (hasOwnProperty.call(template, key)) {
+            map[key] = template[key];
         }
 
         return map;
@@ -412,9 +414,6 @@ namespace ts {
     /**
      * Enumerates the properties of a Map<T>, invoking a callback and returning the first truthy result.
      *
-     * NOTE: This is intended for use with Map<T> objects. For MapLike<T> objects, use
-     *       forEachOwnProperties instead as it offers better runtime safety.
-     *
      * @param map A map for which properties should be enumerated.
      * @param callback A callback to invoke for each property.
      */
@@ -426,53 +425,6 @@ namespace ts {
         return result;
     }
 
-    /**
-     * Enumerates the owned properties of a MapLike<T>, invoking a callback and returning the first truthy result.
-     *
-     * NOTE: This is intended for use with MapLike<T> objects. For Map<T> objects, use
-     *       forEachProperty instead as it offers better performance.
-     *
-     * @param map A map for which properties should be enumerated.
-     * @param callback A callback to invoke for each property.
-     */
-    export function forEachOwnProperty<T, U>(map: MapLike<T>, callback: (value: T, key: string) => U): U {
-        let result: U;
-        for (const key in map) if (hasOwnProperty.call(map, key)) {
-            if (result = callback(map[key], key)) break;
-        }
-        return result;
-    }
-
-    /**
-     * Maps key-value pairs of a map into a new map.
-     *
-     * NOTE: The key-value pair passed to the callback is *not* safe to cache between invocations
-     *       of the callback.
-     *
-     * @param map A map.
-     * @param callback A callback that maps a key-value pair into a new key-value pair.
-     */
-    export function mapPairs<T, U>(map: Map<T>, callback: (entry: [string, T]) => [string, U]): Map<U> {
-        let result: Map<U>;
-        if (map) {
-            result = createMap<U>();
-            let inPair: [string, T];
-            for (const key in map) {
-                if (inPair) {
-                    inPair[0] = key;
-                    inPair[1] = map[key];
-                }
-                else {
-                    inPair = [key, map[key]];
-                }
-
-                const outPair = callback(inPair);
-                result[outPair[0]] = outPair[1];
-            }
-        }
-        return result;
-    }
-
     /**
      * Returns true if a Map<T> has some matching property.
      *
@@ -489,9 +441,6 @@ namespace ts {
     /**
      * Performs a shallow copy of the properties from a source Map<T> to a target MapLike<T>
      *
-     * NOTE: This is intended for use with Map<T> objects. For MapLike<T> objects, use
-     *       copyOwnProperties instead as it offers better runtime safety.
-     *
      * @param source A map from which properties should be copied.
      * @param target A map to which properties should be copied.
      */
@@ -501,21 +450,6 @@ namespace ts {
         }
     }
 
-    /**
-     * Performs a shallow copy of the owned properties from a source map to a target map-like.
-     *
-     * NOTE: This is intended for use with MapLike<T> objects. For Map<T> objects, use
-     *       copyProperties instead as it offers better performance.
-     *
-     * @param source A map-like from which properties should be copied.
-     * @param target A map-like to which properties should be copied.
-     */
-    export function copyOwnProperties<T>(source: MapLike<T>, target: MapLike<T>): void {
-        for (const key in source) if (hasOwnProperty.call(source, key)) {
-            target[key] = source[key];
-        }
-    }
-
     /**
      * Reduce the properties of a map.
      *
@@ -552,72 +486,9 @@ namespace ts {
         return result;
     }
 
-    /**
-     * Counts the properties of a map.
-     *
-     * NOTE: This is intended for use with Map<T> objects. For MapLike<T> objects, use
-     *       countOwnProperties instead as it offers better runtime safety.
-     *
-     * @param map A map whose properties should be counted.
-     * @param predicate An optional callback used to limit which properties should be counted.
-     */
-    export function countProperties<T>(map: Map<T>, predicate?: (value: T, key: string) => boolean) {
-        let count = 0;
-        for (const key in map) {
-            if (!predicate || predicate(map[key], key)) {
-                count++;
-            }
-        }
-        return count;
-    }
-
-    /**
-     * Counts the owned properties of a map-like.
-     *
-     * NOTE: This is intended for use with MapLike<T> objects. For Map<T> objects, use
-     *       countProperties instead as it offers better performance.
-     *
-     * @param map A map-like whose properties should be counted.
-     * @param predicate An optional callback used to limit which properties should be counted.
-     */
-    export function countOwnProperties<T>(map: MapLike<T>, predicate?: (value: T, key: string) => boolean) {
-        let count = 0;
-        for (const key in map) if (hasOwnProperty.call(map, key)) {
-            if (!predicate || predicate(map[key], key)) {
-                count++;
-            }
-        }
-        return count;
-    }
-
-    /**
-     * Performs a shallow equality comparison of the contents of two maps.
-     *
-     * NOTE: This is intended for use with Map<T> objects. For MapLike<T> objects, use
-     *       equalOwnProperties instead as it offers better runtime safety.
-     *
-     * @param left A map whose properties should be compared.
-     * @param right A map whose properties should be compared.
-     */
-    export function equalProperties<T>(left: Map<T>, right: Map<T>, equalityComparer?: (left: T, right: T) => boolean) {
-        if (left === right) return true;
-        if (!left || !right) return false;
-        for (const key in left) {
-            if (!(key in right)) return false;
-            if (equalityComparer ? !equalityComparer(left[key], right[key]) : left[key] !== right[key]) return false;
-        }
-        for (const key in right) {
-            if (!(key in left)) return false;
-        }
-        return true;
-    }
-
     /**
      * Performs a shallow equality comparison of the contents of two map-likes.
      *
-     * NOTE: This is intended for use with MapLike<T> objects. For Map<T> objects, use
-     *       equalProperties instead as it offers better performance.
-     *
      * @param left A map-like whose properties should be compared.
      * @param right A map-like whose properties should be compared.
      */
@@ -670,17 +541,13 @@ namespace ts {
         return result;
     }
 
-    export function extend<T1 extends MapLike<{}>, T2 extends MapLike<{}>>(first: T1 , second: T2): T1 & T2 {
+    export function extend<T1, T2>(first: T1 , second: T2): T1 & T2 {
         const result: T1 & T2 = <any>{};
-        for (const id in first) {
-            if (hasOwnProperty.call(first, id)) {
-                (result as any)[id] = first[id];
-            }
+        for (const id in second) if (hasOwnProperty.call(second, id)) {
+            (result as any)[id] = (second as any)[id];
         }
-        for (const id in second) {
-            if (hasOwnProperty.call(second, id) && !hasOwnProperty.call(result, id)) {
-                (result as any)[id] = second[id];
-            }
+        for (const id in first) if (hasOwnProperty.call(first, id)) {
+            (result as any)[id] = (first as any)[id];
         }
         return result;
     }
diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index ba1994c8141..f9fdd5a1159 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -773,7 +773,7 @@ namespace FourSlash {
         }
 
         public verifyRangesWithSameTextReferenceEachOther() {
-            ts.forEachOwnProperty(this.rangesByText(), ranges => this.verifyRangesReferenceEachOther(ranges));
+            ts.forEachProperty(this.rangesByText(), ranges => this.verifyRangesReferenceEachOther(ranges));
         }
 
         private verifyReferencesWorker(references: ts.ReferenceEntry[], fileName: string, start: number, end: number, isWriteAccess?: boolean, isDefinition?: boolean) {
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index b37a6a90899..94124432780 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -135,7 +135,7 @@ namespace Harness.LanguageService {
 
         public getFilenames(): string[] {
             const fileNames: string[] = [];
-            ts.forEachOwnProperty(this.fileNameToScript, (scriptInfo) => {
+            ts.forEachProperty(this.fileNameToScript, (scriptInfo) => {
                 if (scriptInfo.isRootFile) {
                     // only include root files here
                     // usually it means that we won't include lib.d.ts in the list of root files so it won't mess the computation of compilation root dir.
diff --git a/src/harness/unittests/moduleResolution.ts b/src/harness/unittests/moduleResolution.ts
index ff0151c40a5..09febd2300a 100644
--- a/src/harness/unittests/moduleResolution.ts
+++ b/src/harness/unittests/moduleResolution.ts
@@ -358,7 +358,7 @@ export = C;
         function test(files: Map<string>, options: CompilerOptions, currentDirectory: string, useCaseSensitiveFileNames: boolean, rootFiles: string[], diagnosticCodes: number[]): void {
             const getCanonicalFileName = createGetCanonicalFileName(useCaseSensitiveFileNames);
             if (!useCaseSensitiveFileNames) {
-                files = mapPairs(files, ([fileName, file]) => [getCanonicalFileName(fileName), file]);
+                files = reduceProperties(files, (files, file, fileName) => (files[getCanonicalFileName(fileName)] = file, files), createMap<string>());
             }
 
             const host: CompilerHost = {
diff --git a/src/harness/unittests/reuseProgramStructure.ts b/src/harness/unittests/reuseProgramStructure.ts
index 9f2b0c343c2..60687d34c55 100644
--- a/src/harness/unittests/reuseProgramStructure.ts
+++ b/src/harness/unittests/reuseProgramStructure.ts
@@ -183,7 +183,7 @@ namespace ts {
         }
         else {
             assert.isTrue(cache !== undefined, `expected ${caption} to be set`);
-            assert.isTrue(equalProperties(expectedContent, cache, entryChecker), `contents of ${caption} did not match the expected contents.`);
+            assert.isTrue(equalOwnProperties(expectedContent, cache, entryChecker), `contents of ${caption} did not match the expected contents.`);
         }
     }
 
diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 9887573436e..49f033b9def 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -69,7 +69,7 @@ namespace ts {
     }
 
     function checkMapKeys(caption: string, map: Map<any>, expectedKeys: string[]) {
-        assert.equal(countProperties(map), expectedKeys.length, `${caption}: incorrect size of map`);
+        assert.equal(reduceProperties(map, count => count + 1, 0), expectedKeys.length, `${caption}: incorrect size of map`);
         for (const name of expectedKeys) {
             assert.isTrue(name in map, `${caption} is expected to contain ${name}, actual keys: ${Object.keys(map)}`);
         }
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 9ba243d9704..db9bdd5043b 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -1419,7 +1419,7 @@ namespace ts.server {
                     /*recursive*/ true
                 );
 
-                project.directoriesWatchedForWildcards = reduceOwnProperties(projectOptions.wildcardDirectories, (watchers, flag, directory) => {
+                project.directoriesWatchedForWildcards = reduceProperties(createMap(projectOptions.wildcardDirectories), (watchers, flag, directory) => {
                     if (comparePaths(configDirectoryPath, directory, ".", !this.host.useCaseSensitiveFileNames) !== Comparison.EqualTo) {
                         const recursive = (flag & WatchDirectoryFlags.Recursive) !== 0;
                         this.log(`Add ${ recursive ? "recursive " : ""}watcher for: ${directory}`);
diff --git a/src/services/services.ts b/src/services/services.ts
index 87093645e2a..1153e2e9e3d 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -2058,7 +2058,7 @@ namespace ts {
                 options[opt.name] = parseCustomTypeOption(opt, value, diagnostics);
             }
             else {
-                if (!forEachOwnProperty(opt.type, v => v === value)) {
+                if (!forEachProperty(opt.type, v => v === value)) {
                     // Supplied value isn't a valid enum value.
                     diagnostics.push(createCompilerDiagnosticForInvalidCustomType(opt));
                 }