Rx — If the Operators could speak!
If the RxJS operators could talk, here‘s how they might explain what they do. Understanding the operators is key to leveraging the power of RxJS in your applications.
Creation Operators
These operators are used to create observables from various sources.
create
"I allow you to make an observable from scratch. Tell me when to emit values, when to complete, and when to error. I‘ll handle the subscriptions and do whatever you say!"
of
"I convert the arguments you give me into an observable sequence. Simple as that!"
from
"I can make an observable from an array, a promise, or an iterable like Map and Set. Just pass me any of those things and I‘ll emit their values."
fromEvent
"Pass me a DOM element and event name, and I‘ll create an observable of those events. Super handy for listening to clicks, hovers etc."
interval
"I create an observable that emits incremental numbers periodically at the interval you specify (in milliseconds). Keep me going infinitely or specify how many emissions you want."
timer
"I work just like interval, but you get to specify when I should first emit and the interval for subsequent emissions. You know, in case you don‘t want me blasting off right away."
Transformation Operators
These operators transform the emitted values into different forms or values.
map
"I am the simplest transformation operator. Pass me a projection function, and I‘ll apply it to each value emitted by the source observable. Easy peasy!"
pluck
"I extract a specific nested property from each emitted object. No need for an elaborate map, just tell me the property name and I‘ll pluck those values out for you."
scan
"I am like map‘s accumlating cousin. Pass me an accumulator function and I‘ll invoke it for each emission, passing in the current value and previous return value each time. Useful for things like summation and concatenation."
buffer
"I collect the source observable‘s emissions into buffers rather than emitting them individually. Kind of like scan, but focused on grouping not transformation."
window
"I‘m like buffer‘s sibling – instead collecting values into buffers, I split the source into windows based on time or count, and emit observables instead of values."
concatMap
"I map values like map does, but my projection functions have to return observables. Then I subscribe to each one and concat all their emissions onto a single output observable. Map and flat! "
Filtering Operators
These operators filter or trim emissions in some way.
filter
"Just give me a predicate function, and I‘ll only allow values through that pass the test. Like a good bouncer for your observable!"
take
"You tell me how many values you want. I‘ll allow that many to pass through then complete. Like filter, but based on a set quantity rather than condition."
first
"I literally just emit the first value that comes through then complete. Fastest operator around!"
last
"Opposite of first – you know the drill. Give me that last emission only baby!"
debounce
"Ooh this is a fun one. I make sure an observable waits a certain amount of time between emissions before actually emitting. You know, prevents spamming. Give me a duration!"
throttle
"Similar to debounce – I enforce a minimum time interval between emissions. But I emit the first value immediately rather than waiting. After that, throttle engage!"
Combination Operators
These operators are used to combine multiple observables together.
merge
"The name kinda says it all…pass me multiple observables and I‘ll merge their emissions onto a single stream for you. Simple concatination."
combineLatest
"This one‘s interesting. I combine multiple observables by emitting the latest value from each one whenever ANY of them emit a value. You get a tuple of the latest values."
withLatestFrom
"I work like combineLatest, but I don‘t emit my own source observable‘s emissions – I only emit the latest values from the other observables when my source emits."
concat
"Straightforward chaining of observables. I‘ll subscribe to each one passed to me and concat the emissions in order. Like promise chaining but for observables!"
zip
"Give me multiple observables plus a zip function, and I‘ll invoke it with the latest value from each one, emitting the return value. Highly coordinate observabling."
Multicasting Operators
These operators control how subscriptions and emissions flow through your observables.
share
"Pass me an observable, and I make it automatically share emissions among multiple subscribers. Normally each subscriber has an independent execution…I create one hot observable for all!"
publish
"I turn an ordinary cold observable hot – meaning make it start emitting even without subscribers. But I let you manually connect and disconnect the sharing as needed."
refCount
"I enhance a multicasted observable by tracking its number of subscribers. When subscribers > 0 I connect, and disconnect when count reaches 0. Automatic connection management!"
Error Handling Operators
Because things don‘t always go as planned…
catchError
"Register me on an observable to handle any errors in the pipeline. Pass me an error handler function and I‘ll transform it so errors just keep streaming along."
retry
"You can probably guess what I do. Register me to make an observable resubscribe whenever it errors. Tell me how many retries before giving up!"
retryWhen
"I give you full control over retry logic. Pass me a custom handler observable, and I‘ll re-subscribe whenever that observable emits. Super flexible error handling."
Utility Operators
Some handy utilities to control observable execution.
delay
"Want an observable to wait before emitting values? I got u. Just tell me how long of a delay you want and I‘ll make that happen."
observeOn
"I control what thread your observable emissions and subscriptions happen on. Pass me a scheduler and I take care of the rest!"
subscribeOn
"I‘m like observeOn‘s sister, but I ONLY apply the scheduler to subscription handling. Emissions continue on original scheduler."
timeInterval
"Interested in the time between emissions? Register me on an observable and I‘ll have it emit {value, interval} objects rather than just values. You‘re welcome!"
Conditional Operators
These operators perform boolean logic regarding observables.
defaultIfEmpty
"Don‘t like empty observables? I put a stop to that – just give me a default I should emit if the source completes without spitting anything out."
every
"Feed me a predicate function. I‘ll apply it to the source observable emisisons and only emit TRUE if the predicate passes for EVERY single value."
sequenceEqual
"Give me two observables, I‘ll subscribe to each concurrently and check if all their emissions match EXACTLY – both values and order. I emit TRUE if so, FALSE if any discrepancy."
And there you have it – the operators personified! I hope this gives you a useful mental model for how they work. RxJS is extremely powerful, but also complex – so if the operators could talk, this might help us better understand them. Building intuition for their behavior takes time, but pays dividends in mastering reactive programming.
