TPromise.js -> Promise Class
index.js -> tests
user stories implemented:
A promise is a object with then method
.then, .catch .finally each returns a new promise
once a value is settled on a promise, it stays the same i.e. keeping calling .then on a resolve promise gives you the same value
the function f user passed into TPromise(f), should be called after the entire code runs through
when the _fufill method is called, the async operation succeeded
support chaning
support multiple .then on a promise
handle the case that no function is given for a .then()
if a user gives a promise object p in resolve, we wait for p to resolve and give out the resolved value of p
a promise either fufills or rejects, have machanism making sure only 1 runs
allow .then after .catch
when the function passed in throws an error, promise rejects