defaultdict.js

// Getting defaultdict from Python in JS
class DefaultDict extends Object {
  constructor(defaultInit) {
    return new Proxy({}, {
      get: (target, name) => name in target ?
        target[name] :
        (target[name] = typeof defaultInit === 'function' ?
          new defaultInit().valueOf() :
          defaultInit)
    })
  }
}


// NOTE: [] doesn't work, use Array
d = new DefaultDict([])
d[1].push({foo: 'bar'})
d['zoo'].push({one: 1})
d.zoo
> [ { foo: 'bar' }, { one: 1 } ]
d[1]
> [ { foo: 'bar' }, { one: 1 } ]

s = new DefaultDict(Array)
s[1].push({'foo': 'bar'})
s['zoo'].push({one: 1})
s[1]
> [ { foo: 'bar' } ]
s.zoo
> [ { one: 1 } ]