diff --git a/js/compiler.ts b/js/compiler.ts
index 0462334429b9fe..56dec9dd663478 100644
--- a/js/compiler.ts
+++ b/js/compiler.ts
@@ -469,6 +469,31 @@ export class DenoCompiler
     return moduleMetaData.outputCode;
   }
 
+  /**
+   * TODO:
+   * Incremental compilation of code used in REPL.
+   */
+  incrementalCompile(
+    sourceCode: SourceCode,
+    previousOutput?: OutputCode
+  ): { diagnostics: ts.Diagnostic[], outputCode: OutputCode, additionalCode: OutputCode } {
+        
+    console.log('incrementalCompile', sourceCode, previousOutput);
+      
+    // const service = this._service;
+
+    // TODO:
+    // 1. transpile code to JS
+    // 2. diff code with 'previousOutput'
+    // 3. return new lines and diagnostics
+
+    return {
+      diagnostics: [],
+      outputCode: sourceCode,
+      additionalCode: '',
+    };
+  }
+
   /** Given a fileName, return what was generated by the compiler. */
   getGeneratedContents = (fileName: string): string | RawSourceMap => {
     this._log("compiler.getGeneratedContents", fileName);
diff --git a/js/main.ts b/js/main.ts
index 176f098c760de6..d945f41518cf26 100644
--- a/js/main.ts
+++ b/js/main.ts
@@ -96,6 +96,6 @@ export default function denoMain() {
   if (inputFn) {
     compiler.run(inputFn, `${cwd}/`);
   } else {
-    replLoop();
+    replLoop(`${cwd}/`);
   }
 }
diff --git a/js/repl.ts b/js/repl.ts
index 3139330f6bf696..bf4b74263d9d6f 100644
--- a/js/repl.ts
+++ b/js/repl.ts
@@ -7,6 +7,7 @@ import { close } from "./files";
 import * as dispatch from "./dispatch";
 import { exit } from "./os";
 import { window } from "./globals";
+import { DenoCompiler } from "./compiler";
 
 function startRepl(historyFile: string): number {
   const builder = flatbuffers.createBuilder();
@@ -46,6 +47,21 @@ export function readline(rid: number, prompt: string): string {
   return line || "";
 }
 
+
+interface ReplContext {
+  lines: string[];
+  previousOutput: string;
+}
+
+/**
+ * Eval helpers.
+ */
+// const EVAL_FILENAME = `[eval].ts`
+const REPL_CONTEXT: ReplContext = {
+  lines: [],
+  previousOutput: '',
+};
+
 // @internal
 export function replLoop(): void {
   window.deno = deno; // FIXME use a new scope (rather than window).
@@ -78,8 +94,17 @@ export function replLoop(): void {
 
 function evaluate(code: string): void {
   try {
-    const result = eval.call(window, code); // FIXME use a new scope.
+    // TODO:
+    // 1. preserve context between calls
+    // 2. run only incremental lines, not full output
+    // 3. output diagnostics
+    REPL_CONTEXT.lines.push(code);
+    const compiledCode = compileReplCode(REPL_CONTEXT);
+    console.log('compiledCode', compiledCode);
+
+    const result = eval.call(window, compiledCode.outputCode); // FIXME use a new scope.
     console.log(result);
+    REPL_CONTEXT.previousOutput = compiledCode.outputCode;
   } catch (err) {
     if (err instanceof Error) {
       console.error(`${err.constructor.name}: ${err.message}`);
@@ -89,6 +114,13 @@ function evaluate(code: string): void {
   }
 }
 
+const compiler = DenoCompiler.instance();
+
+function compileReplCode(context: ReplContext) {
+  const sourceCode = context.lines.join('\n');
+  return compiler.incrementalCompile(sourceCode, context.previousOutput);
+}
+
 function readBlock(
   rid: number,
   prompt: string,