Autovivification and Javascript

问题:

Does autovivification only have to do with "derefencing" undefined structures, because in JavaScript if you specify a index or a property that doesn't exist won't it dynamically create it? But is this not autovivification because you must declare the underlying structure to first be an object or an array?

回答1:

Namespacing is one area where autovivification might be handy in JavaScript. Currently to "namespace" an object, you have to do this:

var foo = { bar: { baz: {} } };
foo.bar.baz.myValue = 1;

Were autovivification supported by JavaScript, the first line would not be necessary. The ability to add arbitrary properties to objects in JavaScript is due to its being a dynamic language, but is not quite autovivification.

回答2:

ES6's Proxy can be used for implementing autovivification,

var tree = () => new Proxy({}, { get: (target, name) => name in target ? target[name] : target[name] = tree() });

Test:

var t = tree();
t.bar.baz.myValue = 1;
t.bar.baz.myValue