getValue should support fallback value

[FND]

The TiddlyWiki.prototype.getValue accessor should take an optional argument specifying a default value.

Ideally, this would default to using defaultCustomFields as fallback.

[FND]

Fallback idiom can be used instead:

store.getValue(tiddler, field) || fallback;

[EricShulman]

Replying to FND:

Fallback idiom can be used instead: {{{

store.getValue(tiddler, field) fallback; }}}

When used within a larger expression, you may need additional parentheses to ensure the correct order of operators within the expression, like this:

var foo=....(store.getValue(tiddler, field)||fallback)....;

Although I concur that it is not necessary to add the fallback as a argument passed to getValue, it would reduce the amount of puncuation needed and makes the syntax a little bit cleaner, and thus less prone to programming errors.

var foo=....store.getValue(tiddler, field, fallback)....;

[FND]

Having thought about this a little more myself, there's another drawback to using this idiom: If a value is returned which evaluates to false, the fallback is used erroneously.

While this is currently unlikely to happen (tiddler fields are strings), it should nevertheless be considered.

[FND]

fallback idiom is more explicit