This is an optional appendix to my Twine code shortcuts article. Most of the things here are entirely valid, but aren't as intuitive, and don't really save that much in the way of typing or expression. Nonetheless, they do reveal some underlying concepts to JavaScript that may be enlightening.

Reducing strings and numbers to true and false

In JavaScript, using strings or numbers in place of true, false, or conditional statements such as "x > y" means that the computer will try and convert the strings or numbers into either true or false. The rule for those two types of values is: the number 0 and a string with zero characters in it, "", are converted to false - everything else is converted to true. (0 and "" are called "falsy" values because they're equivalent to false - other values are "truthy").

^{(If you're familiar with Game Maker, you of course know that Game Maker considers all negative numbers to be falsy as well - but not so in JavaScript!)}

This is not really that useful, except for explaining the behaviour of later examples, but it does mean that you could shorten certain <<if>> comparisons:

<<if $hp neq 0>>

can be shortened to

<<if $hp>>

You can also use Not to express the opposite.

<<if $hp eq 0>>

can be validly rewritten as

<<if not $hp>>

false is equivalent to 0, true is equivalent to 1

With regards to numbers, the process of true/false coercion also works symmetrically - the value false, when used in arithmetic, is converted to 0. <<set $red = 3 + false>> is valid, but useless. Nevertheless, this understanding is necessary for the next part.

As a corollary, the raw value true, when used in arithmetic, is converted to 1. This means that <<set $dead += (not $hp)>> will add 1 to $dead if $hp is 0.

And and Or

The way And and Or is implemented in JavaScript is interesting: "x and y" means "if x is false, the value of this statement is x (i.e false), otherwise the value of this statement is y". And, as discussed previously, since such statements are usually used for true/false comparisons, then y is reduced to its true/false value - as one expects.

However, what if you used it in a situation where a plain value was expected? Essentially, it can be used in a manner similar to the ternary operator:

<<set $liveammo = ($gun and $bullets)>>

This line, given the rule above, sets $liveammo to equal $bullets, but only if $gun is true - if not, it's set to false, i.e. 0 (or whatever falsy value $gun has). It may look counterintuitive, especially since it relies on the aforementioned understanding of true/false reduction, but it's equivalent to <<set $liveammo = ($gun ? 0 : $bullets)>>

Or is implemented in JavaScript this way: "x or y" means "if x is true, the value of this statement is x (i.e true), otherwise the value of this statement is y". This means you could use it like this:

<<set $samusenergy = ($energytank or $reservetank)>>

That line only sets $samusenergy to be $reservetank if the $energytank variable is 0. It's equivalent to <<set $samusenergy = ($energytank ? $energytank : $reservetank)>>

It can also be used, in a way, to specify a "default" value if the first value is 0 or an empty string:

<<set $name = ($name or prompt(“What’s your name?”))>>

This line of code will only prompt the player if $name isn't an empty string (i.e. a name was already given).