Simon Oberhammer oberhamsi

true and false vs. "truthy" and "falsey" (or "falsy") in Ruby, Python, and JavaScript

Many programming languages, including Ruby, have native boolean (true and false) data types. In Ruby they're called true and false. In Python, for example, they're written as True and False. But oftentimes we want to use a non-boolean value (integers, strings, arrays, etc.) in a boolean context (if statement, &&, ||, etc.).

This outlines how this works in Ruby, with some basic examples from Python and JavaScript, too. The idea is much more general than any of these specific languages, though. It's really a question of how the people designing a programming language wants booleans and conditionals to work.

If you want to use or share this material, please see the license file, below.

Update

Put a closure on it

Sometimes you'll have objects that manage state along with event handling. This happens frequently in MVC apps. Let's start with a messy example:

var Launcher = function(rocket) {
  this.rocket = rocket
}

Launcher.prototype.isReady = function() {

	var swipeFunc = {
	touches : {
	"touchstart": {"x":-1, "y":-1},
	"touchmove" : {"x":-1, "y":-1},
	"touchend" : false,
	"direction" : "undetermined"
	},
	touchHandler: function(event) {
	var touch;
	if (typeof event !== 'undefined'){

	CXX = g++

	CXXFLAGS = $(shell mapnik-config --cflags) $(shell Magick++-config --cxxflags --cppflags) -Wall
	LDFLAGS = $(shell mapnik-config --libs --dep-libs --ldflags) $(shell Magick++-config --ldflags --libs) -lboost_program_options -lpthread

	OBJ = mapnik_osm_metatiles.o

	BIN = render_mapnik_osm_metatiles

	all : $(BIN)

	<!DOCTYPE html>
	<html>
	<head>
	<title>GameJS Application</title>
	<!-- Styling -->
	<style type=text/css>
	body{
	background:#fff;
	color:#222;
	margin:1em 0 2em 6em;

	/*
	===============================================================================
	A C++ port of a speed-improved simplex noise algorithm for 2D in Java.

	Based on example code by Stefan Gustavson ([email protected]).
	Optimisations by Peter Eastman ([email protected]).
	Better rank ordering method by Stefan Gustavson in 2012.
	C++ port and minor type and algorithm changes by Josh Koch ([email protected]).

	This could be speeded up even further, but it's useful as it is.

	package foo;

	import edu.stanford.nlp.fsm.ExactGrammarCompactor;
	import edu.stanford.nlp.io.IOUtils;
	import edu.stanford.nlp.io.NumberRangeFileFilter;
	import edu.stanford.nlp.io.NumberRangesFileFilter;
	import edu.stanford.nlp.ling.*;
	import edu.stanford.nlp.objectbank.TokenizerFactory;
	import edu.stanford.nlp.parser.ViterbiParser;
	import edu.stanford.nlp.parser.KBestViterbiParser;

	-- show running queries (pre 9.2)
	SELECT procpid, age(clock_timestamp(), query_start), usename, current_query
	FROM pg_stat_activity
	WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%'
	ORDER BY query_start desc;

	-- show running queries (9.2)
	SELECT pid, age(clock_timestamp(), query_start), usename, query
	FROM pg_stat_activity
	WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'

	define([
	"underscore",
	"backbone",
	"marionette",
	"vent"
	],

	/**
	* Creates the primary `Marionette.Application` object that runs the admin framework. Provides a central point
	* from which all other sub-applications are started, shown, hidden, and stopped.