devleague / Calls-from-the-Highest-Order

JS Callback Exercise

Calls from the Highest Order

Callback functions in Javascript

it is highly recommended to have completed Sir-Mix-Alot first.

Goal

Write and invoke callback functions. Practice asynchronous execution in sequence.

Install Dependencies

npm install

Run tests

mocha -w --bail

Callbacks

do all work in lib/callbacks.js

wait

declare a function named wait that accepts two arguments, seconds and callback.

wait will invoke the callback function after n seconds, where n is the value of the seconds argument.

test wait

log the message "wait 3 started".
invoke wait with 3 as the first argument, and an unnamed callback function as the second argument.
the unnamed callback function logs the message "wait 3 done".

the expected behavior is that the first message will be printed out to the console immediately, then the second message will be printed out to the console after 3 seconds.

repeat

declare a function named repeat that accepts two arguments, times and callback.

repeat will invoke the callback function n many times, where n is the value of the times argument.

callback will be invoked with one argument passed in, which is the value of the iteration step in which it was invoked. the first time callback is invoked, 0 will be passed to it, the third time callback is invoked, 2 will be passed to it.

test repeat

invoke the repeat function passing in 10 as the first argument, and a callback function for the second argument.
the callback function accepts one argument, iteration.
the callback function logs the result of adding 100 to the value of iteration.

the expected behavior is that the numbers 100 through 109 will be printed out to the console.

test wait and repeat

Perform the following sequence:

1. wait 4 seconds seconds before continuing to the next step
2. repeat the following steps 2 times
3. log "repeating for i [n]" where [n] is current iteration from repeat
4. wait [n] * 3 seconds before continuing to the next step, where n is the current iteration from repeat
5. repeat the following steps 3 times
6. log the following message "i [n] j [m]" where [n] is the current iteration from step 2. and [m] is the current iteration from step 5.

the expected behavior is that, after 3 seconds, the following will be printed out to the console

wait 3 done
repeating for i 0
repeating for i 1
i 0 j 0
i 0 j 1
i 0 j 2

then after 3 more seconds, this will be printed out to the console

i 1 j 0
i 1 j 1
i 1 j 2

Find Users

1. Import the module found in ./datastore.js
2. Create an empty class named User with a constructor that takes 0 arguments.
3. Add a static method named find to the User class that takes 2 arguments, query and callback
4. the find function will invoke the callback function, passing back all user objects from the datastore, where every key found in the query argument, matches the value of the matching key in the user object from the datastore.
5. if query has a key that does not exist in the imaginary user schema, invoke the callback function passing back a javascirpt RangeError with a very descriptive error message.
6. if query has a key that does exist in the imaginary user schema, however the values of the query param and the user param are of different types, invoke the callback function passing back a javascirpt TypeError with a very descriptive error message.

The callback function signature is function(error, users)
where error is an Error object if there are any errors, else is null
and users is an array containing any users found by the query.

test finding users

Invoke the User.find method with
query : { id : 2 }
callback : function with two parameters, error and users
if the error is not null, throw the error
log a message with 'users' and the users result

the expected result of the callback function is

users [ { id: 2, name: 'goldstine', mood: 'reverent' } ]

---

Invoke the User.find method with
query : { happy : true, iKnowIt : true }
callback : function with two parameters, error and users
if the error is not null, log the error type, ":", and the error message
log a message with 'users' and the users result

the expected result of the callback function is

RangeError : query argument `iKnowIt` is not a property of "User"
users []

---

Invoke the User.find method with
query : { id : 4, name : "davinci" }
callback : function with two parameters, error and users
if the error is not null, throw the error
log a message with 'users' and the users result

the expected result of the callback function is

users [ { id: 4, name: 'davinci', mood: 'elated' } ]

---

Invoke the User.find method with
query : { mood : "elated" }
callback : function with two parameters, error and users
if the error is not null, throw the error
log a message with 'users' and the users result

the expected result of the callback function is

users [ { id: 3, name: 'curie', mood: 'elated' },
  { id: 4, name: 'davinci', mood: 'elated' },
  { id: 5, name: 'mccarthy', mood: 'elated' } ]

---

Invoke the User.find method with
query : { id : "two" }
callback : function with two parameters, error and users
if the error is not null, log the error type, ":", and the error message
log a message with 'users' and the users result

the expected result of the callback function is

TypeError : query arguments are incorrect types, `id` is "string", expected "number"
users []