REPL for WSH JScript

repl.js

(function () {
	var stdin;
	var stdout;
	var stderr;
	var line;
	var command;
	var buffer;
	var inBlock;
	var globalEval;

	if (WScript.FullName.toLowerCase().indexOf("cscript.exe") === -1) {
		WScript.Echo("Run this script with cscript.exe, not wscript.exe.");
		WScript.Quit(1);
	}

	stdin = WScript.StdIn;
	stdout = WScript.StdOut;
	stderr = WScript.StdErr;
	buffer = "";
	inBlock = false;

	stdout.WriteLine("WSH JScript REPL");
	stdout.WriteLine("Commands: .help, .exec, .begin, .end, .abort, .exit");

	while (true) {
		if (inBlock) {
			stdout.Write("...  ");
		} else {
			stdout.Write("js> ");
		}

		try {
			line = stdin.ReadLine();
		} catch (eof) {
			break;
		}

		command = line.replace(/^\s+|\s+$/g, "").toLowerCase();

		if (inBlock) {
			if (command === ".end") {
				executeCode(buffer, true);
				buffer = "";
				inBlock = false;
			} else if (command === ".abort") {
				buffer = "";
				inBlock = false;
				stdout.WriteLine("Block discarded.");
			} else {
				if (buffer !== "") {
					buffer += "\r\n";
				}

				buffer += line;
			}

			continue;
		}

		if (command === ".exit" || command === ".quit") {
			break;
		}

		if (command === ".help") {
			showHelp();
		} else if (command === ".begin") {
			buffer = "";
			inBlock = true;
		} else if (command.indexOf(".exec") === 0 && (command.length === 5 || /\s/.test(command.charAt(5)))) {
			executeCode(line.substring(5).replace(/^\s+/, ""), false);
		} else if (command !== "") {
			executeCode(line, true);
		}
	}

	function executeCode(source, printResult) {
		var result;

		if (source.replace(/^\s+|\s+$/g, "") === "") {
			return;
		}

		try {
			result = eval(source);

			if (printResult && typeof result !== "undefined") {
				stdout.WriteLine(formatValue(result));
			}
		} catch (error) {
			stderr.WriteLine("Error: " + error.name + ": " + error.message);
		}
	}

	function formatValue(value) {
		if (value === null) {
			return "null";
		}

		if (typeof value === "undefined") {
			return "undefined";
		}

		if (typeof value === "string") {
			return value;
		}

		try {
			if (typeof value === "object") {
				return JSON.stringify(value);
			}
		} catch (error) {
			return String(value);
		}

		return String(value);
	}

	function showHelp() {
		stdout.WriteLine("expression       Evaluate code and print its resulting value");
		stdout.WriteLine(".exec code       Execute code without printing a result");
		stdout.WriteLine(".begin           Start a multi-line JavaScript block");
		stdout.WriteLine(".end             Evaluate the buffered block");
		stdout.WriteLine(".abort           Discard the buffered block");
		stdout.WriteLine(".exit / .quit    Leave the REPL");
	}
}());