1 files changed, 197 insertions, 0 deletions
diff --git a/cli/js/repl.ts b/cli/js/repl.ts
new file mode 100644
index 000000000..966e809e8
--- /dev/null
+++ b/cli/js/repl.ts
@@ -0,0 +1,197 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { close } from "./files.ts";
+import { exit } from "./os.ts";
+import { window } from "./window.ts";
+import { core } from "./core.ts";
+import { formatError } from "./format_error.ts";
+import { stringifyArgs } from "./console.ts";
+import * as dispatch from "./dispatch.ts";
+import { sendSync, sendAsync } from "./dispatch_json.ts";
+
+const { console } = window;
+
+/**
+ * REPL logging.
+ * In favor of console.log to avoid unwanted indentation
+ */
+function replLog(...args: unknown[]): void {
+  core.print(stringifyArgs(args) + "\n");
+}
+
+/**
+ * REPL logging for errors.
+ * In favor of console.error to avoid unwanted indentation
+ */
+function replError(...args: unknown[]): void {
+  core.print(stringifyArgs(args) + "\n", true);
+}
+
+const helpMsg = [
+  "_       Get last evaluation result",
+  "_error  Get last thrown error",
+  "exit    Exit the REPL",
+  "help    Print this help message"
+].join("\n");
+
+const replCommands = {
+  exit: {
+    get(): void {
+      exit(0);
+    }
+  },
+  help: {
+    get(): string {
+      return helpMsg;
+    }
+  }
+};
+
+function startRepl(historyFile: string): number {
+  return sendSync(dispatch.OP_REPL_START, { historyFile });
+}
+
+// @internal
+export async function readline(rid: number, prompt: string): Promise<string> {
+  return sendAsync(dispatch.OP_REPL_READLINE, { rid, prompt });
+}
+
+// Error messages that allow users to continue input
+// instead of throwing an error to REPL
+// ref: https://github.com/v8/v8/blob/master/src/message-template.h
+// TODO(kevinkassimo): this list might not be comprehensive
+const recoverableErrorMessages = [
+  "Unexpected end of input", // { or [ or (
+  "Missing initializer in const declaration", // const a
+  "Missing catch or finally after try", // try {}
+  "missing ) after argument list", // console.log(1
+  "Unterminated template literal" // `template
+  // TODO(kevinkassimo): need a parser to handling errors such as:
+  // "Missing } in template expression" // `${ or `${ a 123 }`
+];
+
+function isRecoverableError(e: Error): boolean {
+  return recoverableErrorMessages.includes(e.message);
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type Value = any;
+
+let lastEvalResult: Value = undefined;
+let lastThrownError: Value = undefined;
+
+// Evaluate code.
+// Returns true if code is consumed (no error/irrecoverable error).
+// Returns false if error is recoverable
+function evaluate(code: string): boolean {
+  const [result, errInfo] = core.evalContext(code);
+  if (!errInfo) {
+    lastEvalResult = result;
+    replLog(result);
+  } else if (errInfo.isCompileError && isRecoverableError(errInfo.thrown)) {
+    // Recoverable compiler error
+    return false; // don't consume code.
+  } else {
+    lastThrownError = errInfo.thrown;
+    if (errInfo.isNativeError) {
+      const formattedError = formatError(
+        core.errorToJSON(errInfo.thrown as Error)
+      );
+      replError(formattedError);
+    } else {
+      replError("Thrown:", errInfo.thrown);
+    }
+  }
+  return true;
+}
+
+// @internal
+export async function replLoop(): Promise<void> {
+  Object.defineProperties(window, replCommands);
+
+  const historyFile = "deno_history.txt";
+  const rid = startRepl(historyFile);
+
+  const quitRepl = (exitCode: number): void => {
+    // Special handling in case user calls deno.close(3).
+    try {
+      close(rid); // close signals Drop on REPL and saves history.
+    } catch {}
+    exit(exitCode);
+  };
+
+  // Configure window._ to give the last evaluation result.
+  Object.defineProperty(window, "_", {
+    configurable: true,
+    get: (): Value => lastEvalResult,
+    set: (value: Value): Value => {
+      Object.defineProperty(window, "_", {
+        value: value,
+        writable: true,
+        enumerable: true,
+        configurable: true
+      });
+      console.log("Last evaluation result is no longer saved to _.");
+    }
+  });
+
+  // Configure window._error to give the last thrown error.
+  Object.defineProperty(window, "_error", {
+    configurable: true,
+    get: (): Value => lastThrownError,
+    set: (value: Value): Value => {
+      Object.defineProperty(window, "_error", {
+        value: value,
+        writable: true,
+        enumerable: true,
+        configurable: true
+      });
+      console.log("Last thrown error is no longer saved to _error.");
+    }
+  });
+
+  while (true) {
+    let code = "";
+    // Top level read
+    try {
+      code = await readline(rid, "> ");
+      if (code.trim() === "") {
+        continue;
+      }
+    } catch (err) {
+      if (err.message === "EOF") {
+        quitRepl(0);
+      } else {
+        // If interrupted, don't print error.
+        if (err.message !== "Interrupted") {
+          // e.g. this happens when we have deno.close(3).
+          // We want to display the problem.
+          const formattedError = formatError(core.errorToJSON(err));
+          replError(formattedError);
+        }
+        // Quit REPL anyways.
+        quitRepl(1);
+      }
+    }
+    // Start continued read
+    while (!evaluate(code)) {
+      code += "\n";
+      try {
+        code += await readline(rid, "  ");
+      } catch (err) {
+        // If interrupted on continued read,
+        // abort this read instead of quitting.
+        if (err.message === "Interrupted") {
+          break;
+        } else if (err.message === "EOF") {
+          quitRepl(0);
+        } else {
+          // e.g. this happens when we have deno.close(3).
+          // We want to display the problem.
+          const formattedError = formatError(core.errorToJSON(err));
+          replError(formattedError);
+          quitRepl(1);
+        }
+      }
+    }
+  }
+}