evented-chain

Chain async callbacks together; monitor progress with events

example

var chain = require('evented-chain')

function double (x, cb) {
    cb(null, x * 2)
}

function square (x, cb) {
    cb(null, x*x)
}

var doubleSquare = chain(double, square)

doubleSquare(2, function (err, result) { console.log('callback got ' + result) })
    .on('step', function (step, args) {
        console.log('step '+step, 'result: ' + args[0])
    })
    .on('complete', function (args) {
        console.log('final value: ' + args[0])
    })

api

var chain = require('evented-chain')

fn = chain(fn1, fn2, fn3, ...)

chain returns a function (fn), that when called will execute the chained functions (fn1, fn2, ...) in a waterfall manner, where the result of previous functions are fed as arguments to the next function, until all functions have executed. Each function in the chain (fn1, fn2, etc) must accept an error-first style callback as it's last argument, and supply it's result to that callback.

Once the chain has completed executing, the final result will be passed to the (optional) callback provided to the generated function, fn.

If an error is passed to any callback, the final callback (fn) will be executed with the error immediately.

fn = chain([fn1, fn2, fn3, ...])

Same as above, but chain functions may be supplied to chain in an array instead of as arguments.

events

var progress = fn()

When the generated function is executed, an event emitter is returned. This emitter can be listened to for insight into the progress of the chain. Events emitted are:

• step - For each chain function execited succesfully, this event is emitted with step, and args where step is the index of the function executed, and args is an array of arguments passed to that function.
• fail - Emitted when a function executes it's callback with an error. This event is emitetd with step, err, and args where err contains the error passed to the callback, and args contains any other args passed.
• complete - Emitted once the chain has finished executing. This event is emitted with args which contains an array of arguments passed to the final callback, minus the first (non-existant error) argument.

testing

npm test [--dot | --spec] [--coverage]

options

• --dot - output test results as dots instead of tap
• --spec - output test results as spec instead of tap
• --coverage - display text cover report

patterns

Only run test files matching a certain pattern by prefixing the test command with grep=pattern. Example:

grep=connect npm test --dot

html coverage report

Open it with npm run view-cover or npm run vc