Optimize json output by adding toJSON()

[sfescape]

You can reduce the size of the JSON output significantly just by dropping the subCounter field as well as empty children fields.

toJSON() {
return JSON.stringify(this, function(key, value) {
return key === 'subCounter' || (key === 'children' && value.length === 0) ? undefined : value
})
}

You would need to add a check for children in fromJSON to either default children to [] or skip processing children if the field is undefined.