--- title: "Delayed" language: "en" type: "Symbol" summary: "Delayed[expr] represents an expression whose evaluation is delayed until its value is externally requested. Delayed[expr, fmt] specifies that the result from evaluating expr should be given in format fmt. Delayed[expr, {fmt, rform}] specifies that the result should be given as a response of the form rform." keywords: - browser refresh - web computation - dashboard - status display canonical_url: "https://reference.wolfram.com/language/ref/Delayed.html" source: "Wolfram Language Documentation" related_guides: - title: "Cloud Functions & Deployment" link: "https://reference.wolfram.com/language/guide/CloudFunctionsAndDeployment.en.md" - title: "Web Operations" link: "https://reference.wolfram.com/language/guide/WebOperations.en.md" - title: "Automated Reports" link: "https://reference.wolfram.com/language/guide/AutomatedReports.en.md" - title: "HTTP Requests & Responses" link: "https://reference.wolfram.com/language/guide/HTTPRequestsAndResponses.en.md" related_workflows: - title: "Set Up a Web Gallery" link: "https://reference.wolfram.com/language/workflow/SetUpAWebGallery.en.md" related_functions: - title: "Dynamic" link: "https://reference.wolfram.com/language/ref/Dynamic.en.md" - title: "RuleDelayed" link: "https://reference.wolfram.com/language/ref/RuleDelayed.en.md" - title: "APIFunction" link: "https://reference.wolfram.com/language/ref/APIFunction.en.md" - title: "Defer" link: "https://reference.wolfram.com/language/ref/Defer.en.md" - title: "ExportForm" link: "https://reference.wolfram.com/language/ref/ExportForm.en.md" - title: "ResponseForm" link: "https://reference.wolfram.com/language/ref/ResponseForm.en.md" - title: "AutoRefreshed" link: "https://reference.wolfram.com/language/ref/AutoRefreshed.en.md" - title: "DocumentGenerator" link: "https://reference.wolfram.com/language/ref/DocumentGenerator.en.md" --- # Delayed Delayed[expr] represents an expression whose evaluation is delayed until its value is externally requested. Delayed[expr, fmt] specifies that the result from evaluating expr should be given in format fmt. Delayed[expr, {fmt, rform}] specifies that the result should be given as a response of the form rform. ## Details and Options * ``Delayed`` is typically used with ``CloudDeploy`` to create a web page whose content is updated whenever the page is requested. * The following options can be given: | | | | | --------------------------- | -------- | ------------------------------------------------ | | AllowedCloudExtraParameters | None | what overall parameters to allow to be specified | | CachePersistence | 0 | how long to maintain a cache of results | | UpdateInterval | Infinity | how often a browser should request an update | * With the option ``UpdateInterval -> t``, ``Delayed`` specifies that a web page should be updated in the web browser every ``t`` seconds when it is displayed. * The option ``AllowedCloudExtraParameters`` specifies what additional query parameters governing evaluation of ``expr`` should be allowed. * Possible result formats ``fmt`` in ``Delayed[expr, fmt]`` are: | | | | ----- | ------------------------------------------- | | "fmt" | any format supported by ExportForm | | fun | an arbitrary function to be applied to expr | * ``Delayed[expr, "fmt"]`` is equivalent to ``Delayed[ExportForm[expr, "fmt"]]``. * ``Delayed`` is also used to control the resource copying behavior of cloud functions such as ``DocumentGenerator``. Files and cloud objects qualified as ``Delayed`` are used in place. ## Examples (6) ### Basic Examples (3) ``Delayed`` specifies that the expression should not be evaluated until it is requested: ```wl In[1]:= obj = CloudDeploy[Delayed[DateString[]]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/6a65c712-e1a1-4fd0-b9eb-90880145870a"] ``` Visit the link to view the deployed output: ```wl [image] ``` --- Deploy a delayed evaluation that is converted to the ``"CSV"`` format: ```wl In[1]:= obj = CloudDeploy[Delayed[RandomInteger[{1, 10}, {3, 7}], "CSV"]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/01e4b37c-fe38-4edc-ab93-5dcf8a083dce"] ``` Request the object from the cloud: ```wl In[2]:= data = URLRead[obj, "Body"] Out[2]= "3,1,6,8,10,3,3 6,6,6,3,7,8,9 9,8,8,1,8,6,3 " ``` --- Deployed a delayed evaluation where the result is in the ``"CSV"`` format, but the overall response, with fields from ``EvaluationData``, is given in JSON: ```wl In[1]:= obj = CloudDeploy[Delayed[RandomInteger[{1, 10}, {3, 7}], {"CSV", "JSON"}]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/1e5f6299-f250-4260-a60e-a47d55365c37"] ``` Request the object: ```wl In[2]:= URLRead[obj, "Body"] Out[2]= "{ \"StatusCode\":200, \"Success\":true, \"FailureType\":null, \"OutputLog\":[], \"Timing\":6.8e-2, \"AbsoluteTiming\":8.2e-2, \"Messages\":[], \"MessagesText\":[], \"MessagesExpressions\":[], \"InputString\":\"GenerateHTTPResponse[Delaye ... {}|>]\", \"Result\":\"4,1,7,8,3,5,2\ 8,1,10,10,5,4,6\ 8,2,4,8,2,9,2\ \", \"ResultMeta\":{ \"StatusCode\":200, \"ContentType\":\"text\\/csv;charset=iso-8859-1\", \"Headers\":{ \"content-type\":\"text\\/csv;charset=iso-8859-1\" } } }" ``` ### Options (2) #### CachePersistence (1) Deploy a ``Delayed`` that gives the current time and caches its result for up to 3 seconds: ```wl In[1]:= obj = CloudDeploy[Delayed[Now, "Text", CachePersistence -> Quantity[3, "Seconds"]]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/2c3b0ed0-94f8-4306-9981-a17b76a03322"] In[2]:= Table[Pause[1];URLExecute[obj], {5}] Out[2]= {DateObject[{2023, 5, 4, 13, 18, 11.442049}, "Instant", "Gregorian", -5.], DateObject[{2023, 5, 4, 13, 18, 11.442049}, "Instant", "Gregorian", -5.], DateObject[{2023, 5, 4, 13, 18, 11.442049}, "Instant", "Gregorian", -5.], DateObject[{2023, 5, 4, 13, 18, 15.195423}, "Instant", "Gregorian", -5.], DateObject[{2023, 5, 4, 13, 18, 15.195423}, "Instant", "Gregorian", -5.]} ``` #### UpdateInterval (1) Deploy a ``Delayed`` that refreshes every 3 seconds when displayed in a web browser: ```wl In[1]:= CloudDeploy[Delayed[Now, "Text", UpdateInterval -> 3]] Out[1]= CloudObject["https://www.wolframcloud.com/obj/98e2994d-cf7d-4441-9b1a-d038d68bf474"] ``` ### Possible Issues (1) Since the default ``ExportForm`` of ``Delayed[expr]`` is ``HTMLFragment``, an expression evaluating to ``None`` will be returned as an empty string: ```wl In[1]:= computation = CloudPublish[Delayed[None]]; URLExecute[First[computation]] Out[1]= "" ``` In order to get the correct value in the above example, specify the format of ``Delayed[expr]`` as Wolfram Language: ```wl In[2]:= computation = CloudPublish[Delayed[None, "WL"]]; URLExecute[First[computation]] Out[2]= "None" ``` ## See Also * [`Dynamic`](https://reference.wolfram.com/language/ref/Dynamic.en.md) * [`RuleDelayed`](https://reference.wolfram.com/language/ref/RuleDelayed.en.md) * [`APIFunction`](https://reference.wolfram.com/language/ref/APIFunction.en.md) * [`Defer`](https://reference.wolfram.com/language/ref/Defer.en.md) * [`ExportForm`](https://reference.wolfram.com/language/ref/ExportForm.en.md) * [`ResponseForm`](https://reference.wolfram.com/language/ref/ResponseForm.en.md) * [`AutoRefreshed`](https://reference.wolfram.com/language/ref/AutoRefreshed.en.md) * [`DocumentGenerator`](https://reference.wolfram.com/language/ref/DocumentGenerator.en.md) ## Related Guides * [Cloud Functions & Deployment](https://reference.wolfram.com/language/guide/CloudFunctionsAndDeployment.en.md) * [Web Operations](https://reference.wolfram.com/language/guide/WebOperations.en.md) * [Automated Reports](https://reference.wolfram.com/language/guide/AutomatedReports.en.md) * [HTTP Requests & Responses](https://reference.wolfram.com/language/guide/HTTPRequestsAndResponses.en.md) ## Related Workflows * [Set Up a Web Gallery](https://reference.wolfram.com/language/workflow/SetUpAWebGallery.en.md) ## Related Links * [An Elementary Introduction to the Wolfram Language: Creating Websites and Apps](https://www.wolfram.com/language/elementary-introduction/36-creating-websites-and-apps.html) * [An Elementary Introduction to the Wolfram Language: Immediate and Delayed Values](https://www.wolfram.com/language/elementary-introduction/39-immediate-and-delayed-values.html) ## History * [Introduced in 2014 (10.0)](https://reference.wolfram.com/language/guide/SummaryOfNewFeaturesIn100.en.md) \| [Updated in 2014 (10.0.2)](https://reference.wolfram.com/language/guide/SummaryOfNewFeaturesIn100.en.md)