luau-promise/lib

title

docs

Promise

desc types properties functions A Promise is an object that represents a value that will exist in the future, but doesn't right now. Promises allow you to then attach callbacks that can run once the value becomes available (known as *resolving*), or if an error has occurred (known as *rejecting*). name desc kind type PromiseStatus An enum value used to represent the Promise's status. enum Started Resolved Rejected Cancelled desc The Promise is executing, and not settled yet. desc The Promise finished successfully. desc The Promise was rejected. desc The Promise was cancelled before it finished. name tags type desc Status read only static enums PromiseStatus A table containing all members of the `PromiseStatus` enum, e.g., `Promise.Status.Resolved`. name tags desc static params returns new constructor Construct a new Promise that will be resolved or rejected with the given callbacks. ::: tip If your Promise executor needs to yield, it is recommended to use Promise.async instead. You cannot directly yield inside the `executor` function of Promise.new. ::: If you `resolve` with a Promise, it will be chained onto. You may register an optional cancellation hook by using the `onCancel` argument. * This should be used to abort any ongoing operations leading up to the promise being settled. * Call the `onCancel` function with a function callback as its only argument to set a hook which will in turn be called when/if the promise is cancelled. * `onCancel` returns `true` if the Promise was already cancelled when you called `onCancel`. * Calling `onCancel` with no argument will not override a previously set cancellation hook, but it will still return `true` if the Promise is currently cancelled. * You can set the cancellation hook at any time before resolving. * When a promise is cancelled, calls to `resolve` or `reject` will be ignored, regardless of if you set a cancellation hook or not. true name type executor kind params function name type resolve kind params returns function name type ... ...any? void name type reject kind params returns function name type ... ...any? void name type onCancel kind params returns function name kind abortHandler function type desc boolean Returns `true` if the Promise was already cancelled at the time of calling `onCancel`. Promise name tags desc static params returns async constructor The same as Promise.new, except it allows yielding. Use this if you want to yield inside your Promise body. If your Promise body does not need to yield, such as when attaching `resolve` to an event listener, you should use Promise.new instead. ::: tip Promises created with Promise.async don't begin executing until the next `RunService.Heartbeat` event, even if the executor function doesn't yield itself. This is to ensure that Promises produced from a function are either always synchronous or always asynchronous. <a href="/roblox-lua-promise/lib/Details.html#yielding-in-promise-executor">Learn more</a> ::: ```lua local function waitForChild(instance, childName, timeout) return Promise.async(function(resolve, reject) local child = instance:WaitForChild(childName, timeout) ;(child and resolve or reject)(child) end) end ``` true name type asyncExecutor kind params function name type resolve kind params returns function name type ... ...any? void name type reject kind params returns function name type ... ...any? void name type onCancel kind params returns function name kind abortHandler function type desc boolean Returns `true` if the Promise was already cancelled at the time of calling `onCancel`. Promise name desc static params returns promisify Wraps a function that yields into one that returns a Promise. ```lua local sleep = Promise.promisify(wait) sleep(1):andThen(print) ``` ```lua local isPlayerInGroup = Promise.promisify(function(player, groupId) return player:IsInGroup(groupId) end) ``` true name type function kind params function ...: ...any? desc type The function acts like the passed function but now returns a Promise of its return values. kind params returns function name type desc ... ...any? The same arguments the wrapped function usually takes. name desc * The return values from the wrapped function. name desc static params returns resolve Creates an immediately resolved Promise with the given value. true value: T Promise<T> name desc static params returns reject Creates an immediately rejected Promise with the given value. true value: T Promise<T> name desc static params returns all Accepts an array of Promises and returns a new promise that: * is resolved after all input promises resolve. * is rejected if ANY input promises reject. Note: Only the first return value from each promise will be present in the resulting array. true promises: array<Promise<T>> Promise<array<T>> name desc static params returns race Accepts an array of Promises and returns a new promise that is resolved or rejected as soon as any Promise in the array resolves or rejects. All other Promises that don't win the race will be cancelled. true promises: array<Promise<T>> Promise<T> name desc static params returns is Returns whether the given object is a Promise. true object: any type desc boolean `true` if the given `object` is a Promise. name desc params returns overloads andThen Chains onto an existing Promise and returns a new Promise. Return a Promise from the success or failure handler and it will be chained onto. name type successHandler kind params returns function ...: ...any? ...any? name optional type failureHandler true kind params returns function ...: ...any? ...any? Promise<...any?> params returns name type successHandler kind params returns function ...: ...any? Promise<T> name optional type failureHandler true kind params returns function ...: ...any? Promise<T> Promise<T> name desc params returns overloads catch Shorthand for `Promise:andThen(nil, failureHandler)`. name type failureHandler kind params returns function ...: ...any? ...any? Promise<...any?> params returns name type failureHandler kind params returns function ...: ...any? Promise<T> Promise<T> name desc params returns overloads finally Set a handler that will be called regardless of the promise's fate. The handler is called when the promise is resolved, rejected, *or* cancelled. Returns a new promise chained from this promise. name type finallyHandler kind params returns function status: PromiseStatus ...any? Promise<...any?> params returns name type finallyHandler kind params returns function status: PromiseStatus Promise<T> Promise<T> name desc params returns andThenCall Attaches an `andThen` handler to this Promise that calls the given callback with the predefined arguments. The resolved value is discarded. ```lua promise:andThenCall(someFunction, "some", "arguments") ``` This is sugar for ```lua promise:andThen(function() return someFunction("some", "arguments") end) ``` name type callback kind params returns function ...: ...any? any name type desc ... ...any? Arguments which will be passed to the callback. Promise name desc params returns finallyCall Same as `andThenCall`, except for `finally`. Attaches a `finally` handler to this Promise that calls the given callback with the predefined arguments. name type callback kind params returns function ...: ...any? any name type desc ... ...any? Arguments which will be passed to the callback. Promise name desc cancel Cancels this promise, preventing the promise from resolving or rejecting. Does not do anything if the promise is already settled. Cancellations will propagate upwards through chained promises. Promises will only be cancelled if all of their consumers are also cancelled. This is to say that if you call `andThen` twice on the same promise, and you cancel only one of the child promises, it will not cancel the parent promise until the other child promise is also cancelled. name desc returns await Yields the current thread until the given Promise completes. Returns true if the Promise resolved, followed by the values that the promise resolved or rejected with. ::: warning If the Promise gets cancelled, this function will return `false`, which is indistinguishable from a rejection. If you need to differentiate, you should use Promise.awaitStatus instead. ::: desc type `true` if the Promise successfully resolved. boolean desc type The values that the Promise resolved or rejected with. ...any? name desc returns awaitStatus Yields the current thread until the given Promise completes. Returns the Promise's status, followed by the values that the promise resolved or rejected with. type desc PromiseStatus The Promise's status. type desc ...any? The values that the Promise resolved or rejected with. name desc returns awaitValue Yields the current thread until the given Promise completes. Returns the the values that the promise resolved with. Errors if the Promise rejects or gets cancelled. type desc ...any? The values that the Promise resolved with. name desc returns getStatus Returns the current Promise status. PromiseStatus