Exception in TS if @observable has no initializer

[farwayer]

If you try to observe (intercept, ...) property without initial value before first access then you will get exception. I think we need to add runLazyInitializers to TS also. Or even rewrite logic to make init more consistency between TS and JS. It's really bit hacky now.

import {observable, observe} from 'mobx'

class User {
  @observable
  loginCount;
}

const user = new User();
observe(user, 'loginCount', () => {});

tsc --experimentalDecorators test.ts

/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:2211
        throw new Error("[mobx] Invariant failed: " + message + (thing ? " in '" + thing + "'" : ""));
        ^

Error: [mobx] Invariant failed: Cannot obtain atom from [object Object]
    at invariant (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:2211:15)
    at fail (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:2206:5)
    at getAtom (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:3129:12)
    at getAdministration (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:3134:34)
    at observeObservableProperty (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:3178:12)
    at Object.observe (/mnt/data/dev/react/mobx-decorators/node_modules/mobx/lib/mobx.js:3170:16)
    at Object.<anonymous> (/mnt/data/dev/react/mobx-decorators/test.js:19:8)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)

[mweststrate]

Can you set up a reproduction? Ideally a PR with an additional typescript unit test?

[mweststrate]

Released fix as 3.1.17