require(["esri/core/promiseUtils"], (promiseUtils) => { /* code goes here */ });
import * as promiseUtils from "@arcgis/core/core/promiseUtils.js";
esri/core/promiseUtils
Various utilities and convenience functions for working with promises.
Method Overview
Name | Return Type | Summary | Object |
---|---|---|---|
Creates a special error object which is used to signal aborted requests in promise chains. | promiseUtils | ||
A utility for ensuring an input function is not simultaneously invoked more than once at a time. | promiseUtils | ||
Convenience utility method to wait for a number of promises to either resolve or reject. | promiseUtils | ||
A convenience utility method for filtering an array of values using an asynchronous predicate function. | promiseUtils | ||
Check if the provided error object is the special kind of error with which promises are rejected when they are aborted. | promiseUtils |
Method Details
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createAbortError
createAbortError(){Error}
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Creates a special error object which is used to signal aborted requests in promise chains. Promises that are rejected due to abort signals should reject with this kind of error.
ReturnsType Description Error A special error object that signals an aborted request. Example// Request multiple files and return results in an array function requestMultiple(urls, abortSignal) { // Fire off requests let promises = urls.map(url => request(url, { signal: abortSignal }); // Wait until all requests have either resolved or rejected promiseUtils.eachAlways(urls) .then(results => { if (abortSignal && abortSignal.aborted) { // If the user has triggered the abortSignal, all requests will react and reject. eachAlways resolves with // an array that contains the reject error for each request. Instead of returning this array as a result, we // should reject the promise returned to the user with an abort error. throw promiseUtils.createAbortError(); } return results; }); }
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debounce
debounce(callback){Function}static
Since: ArcGIS Maps SDK for JavaScript 4.12promiseUtils since 4.2, debounce added at 4.12. -
A utility for ensuring an input function is not simultaneously invoked more than once at a time. This is useful for highly interactive applications such as those that execute statistic queries on mouse-move or mouse-drag events. Rather than execute the query for each such event, you can "debounce", or cancel the function execution, until the previous execution of the same function call finishes. This improves the performance and user experience of such applications.
Parametercallback FunctionA function to prevent executing during the execution of a previous call to the same function. This is typically a function that may be called on mouse-move or mouse-drag events.
ReturnsType Description Function A function with the same signature as the callback. - See also
Example// Queries a layer for the count of features that intersect a // 1 km buffer of the pointer location. The debounce() method // prevents the updateStatistics function from executing before // a previous invocation of the same function finishes. const updateStatistics = promiseUtils.debounce(function (geometry) { return layerView.queryFeatures({ geometry, distance: 1, units: "kilometers", outStatistics: [{ onStatisticField: "*", outStatisticFieldName: "feature_count", statisticType: "count" }] }).then(function(featureSet) { console.log(`Feature Count: ${featureSet.features[0].attributes["feature_count"]}`); }); }); view.on("drag", (event) => updateStatistics(view.toMap(event)));
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eachAlways
eachAlways(promises){Promise}
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Convenience utility method to wait for a number of promises to either resolve or reject. The resulting promise resolves to an array of result objects containing the promise and either a value if the promise resolved, or an error if the promise rejected. This is similar to the native
Promise.allSettled
method with the additional feature of taking an object parameter.ReturnsType Description Promise If called with an array of promises, resolves to an array of result objects containing the original promise and either a value (if the promise resolved) or an error (if the promise rejected). If called with an object where each property is a promise, then resolves to an object with the same properties where each property value is a result object. Exampleconst controller = new AbortController(); // Query for the number of features from // multiple feature layers function queryLayerFeatureCount(whereClauses) { // pass each whereClause item into callback function return promiseUtils.eachAlways(whereClauses.map(function (whereClause) { return layer.queryFeatureCount(whereClause, { signal: controller.signal }); })); } queryLayerFeatureCount(whereClauses).then(function(eachAlwaysResults) { eachAlwaysResults.forEach(function(result) { // If a Promise was rejected, you can check for the rejected error if (result.error) { console.log("There was an error in your query.", result.error); } // The results of the Promise are returned in the value property else { console.log("The number of features are: " + result.value); } }); });
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filter
filter(input, predicate){Promise}
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A convenience utility method for filtering an array of values using an asynchronous predicate function.
Parametersinput ArrayThe array of input values to filter.
predicate FilterPredicateCallbackA predicate function returning a promise. Only array entries for which the returned promise contains
true
are kept.ReturnsType Description Promise A promise containing an array of values that passed the predicate check.
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isAbortError
isAbortError(error){Boolean}
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Check if the provided error object is the special kind of error with which promises are rejected when they are aborted.
Parametererror ErrorThe error object to test.
ReturnsType Description Boolean true
if the error is an abort error,false
otherwise.Example// This function fetches a document via HTTP and logs its content to the console once available function logHTTPDocumentToConsole(url, abortSignal) { // Pass the abort signal into `request` to make it cancelable request(url, { signal: abortSignal }) .then((response) => { console.log(response.data); }) .catch((error) => { if (!promiseUtils.isAbortError(error)) { // Only log request failures and ignore cancellations console.error("request error", error); } }); } let controller = new AbortController(); let url = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Census/MapServer"; logHTTPDocumentToConsole(url, controller.signal); // Cancel the request controller.abort();
Type Definitions
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EachAlwaysResult
EachAlwaysResult Object
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The result object for a promise passed to promiseUtils.eachAlways.
- Properties
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promise Promise
The promise that has been fulfilled.
value *The value with which the promise resolved. Defined only if the promise resolved.
error *The error with which the promise rejected. Defined only if the promise rejected.
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A function that defines how a promise created in create() is resolved and rejected.
Parametersresolve ResolveCallbackA function that will fulfill the promise.
reject RejectCallbackA function that will handle the rejection of the promise.
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FilterPredicateCallback
FilterPredicateCallback(value, index){Promise}
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Callback to be called for each entry of an array to be filtered.
Parametersvalue *The value of the array entry.
index NumberThe index of the entry within the array.
ReturnsType Description Promise A promise that resolves to a boolean value, indicating whether the entry should be kept in the filtered array.
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A function that will reject the promise created in create().
Parametererror *optionalThe error with which the promise rejected. Defined only if the promise is rejected.