Is there a library to support autovivification on Javascript objects?

Question

Is there anyway, either natively or through a library, to use autovivification on Javascript objects?

IE, assuming foo is an object with no properties, being able to just do foo.bar.baz = 5 rather than needing foo.bar = {}; foo.bar.baz = 5.

Answer 1

You can't do it exactly with the syntax you want. But as usual, in JS you can write your own function:

function set (obj,keys,val) {
    for (var i=0;i<keys.length;i++) {
        var k = keys[i];
        if (typeof obj[k] == 'undefined') {
            obj[k] = {};
        }
        obj = obj[k];
    }
    obj = val;
}

so now you can do this:

// as per you example:
set(foo,['bar','baz'],5);

without worrying if bar or baz are defined. If you don't like the [..] in the function call you can always iterate over the arguments object.

Answer 2

Purely natively, I don't think so. undefined isn't extensible or changeable and that's about the only way I could imagine doing it without passing it through a function.