vantage/lib/intercept.js

"use strict";

/**
 * Module dependencies.
 */

var _	= require("lodash");

/**
 * Intercepts stdout, passes thru callback
 * also pass console.error thru stdout so it goes to callback too
 * (stdout.write and stderr.write are both refs to the same stream.write function)
 * returns an unhook() function, call when done intercepting
 *
 * @param {Function} callback
 * @return {Function}
 */

module.exports = function (callback) {

	var oldStdoutWrite = process.stdout.write,
	oldConsoleError = console.error;

	process.stdout.write = (function(write) {
		return function(string) {
			var args = _.toArray(arguments);
			args[0] = interceptor( string );
			write.apply(process.stdout, args);
		};
	}(process.stdout.write));

	console.error = (function() {
		return function() {
			var args = _.toArray(arguments);
			args.unshift("\x1b[31m[ERROR]\x1b[0m");
			console.log.apply(console.log, args);
		};
	}(console.error));

	function interceptor(string) {
		// only intercept the string
		var result = callback(string);
		if (typeof result === "string") {
			string = result.replace( /\n$/, "" ) + (result && (/\n$/).test( string ) ? "\n" : "");
		}
		return string;
	}

	// puts back to original
	return function unhook() {
		process.stdout.write = oldStdoutWrite;
		console.error = oldConsoleError;
	};

};