promiseUtils

Method Overview

Method Details

create(executor){Promise}

Deprecated since version 4.24. Use Promise instead.

Convenience utility method for creating and resolving a promise.

Parameter

executor Executor A function that will be called with two methods, resolve and reject.

Returns

Type	Description
Promise	A promise that will be fulfilled by the executor.

Examples

function fetchImage(url) {
  return promiseUtils.create(function(resolve, reject){
    const image = document.createElement("img");
    image.onload = function() {
      image.load = image.onerror = null;
      resolve(image);
    };

    image.onerror = function() {
      image.load = image.onerror = null;
      reject(new Error("Error while loading the image"));
    }

    image.src = url;
  });
}

fetchImage(".........")
  .then(function(image){
    console.log(image);
  });

// Load multiple modules conditionally
require([
  "esri/core/promiseUtils"
], function( promiseUtils ) {
  // load modules based on whether a user selects
  // a UI option to apply class breaks to a layer
  if (classBreaksSelected) {
    return promiseUtils.create(function(resolve, reject) {
      require([ "esri/renderers/ClassBreaksRenderer" ], resolve);
    }).then(function(ClassBreaksRenderer) {
      // Create renderer and apply it to the desired layer

    });
  }
});

createAbortError(){Error}

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.

Returns

Type	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;
  });
}

debounce(callback){Function}static

Since: ArcGIS Maps SDK for JavaScript 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.

Parameter

callback Function A 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.

Returns

Type	Description
Function	A function with the same signature as the callback.

See also

• Samples that use debounce() method

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)));

eachAlways(promises){Promise|Object}

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.

Parameter

promises Promise[]|Object Array of promises, or object where each property is a promise.

Returns

Type	Description
Promise | Object	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.

Example

const 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);
     }
   });
});

filter(input, predicate){Promise}

A convenience utility method for filtering an array of values using an asynchronous predicate function.

Parameters

input Array The array of input values to filter.

predicate FilterPredicateCallback A predicate function returning a promise. Only array entries for which the returned promise contains true are kept.

Returns

Type	Description
Promise	A promise containing an array of values that passed the predicate check.

isAbortError(error){Boolean}

Check if the provided error object is the special kind of error with which promises are rejected when they are aborted.

Parameter

error Error The error object to test.

Returns

Type	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

EachAlwaysResult Object

The result object for a promise passed to promiseUtils.eachAlways.

Properties

promise Promise The promise that has been fulfilled.

value * optional The value with which the promise resolved. Defined only if the promise resolved.

error * optional The error with which the promise rejected. Defined only if the promise rejected.

Executor(resolve, reject)

A function that defines how a promise created in create() is resolved and rejected.

Parameters

resolve ResolveCallback A function that will fulfill the promise.

reject RejectCallback A function that will handle the rejection of the promise.

FilterPredicateCallback(value, index){Promise}

Callback to be called for each entry of an array to be filtered.

Parameters

value * The value of the array entry.

index Number The index of the entry within the array.

Returns

Type	Description
Promise	A promise that resolves to a boolean value, indicating whether the entry should be kept in the filtered array.

RejectCallback(error)

A function that will reject the promise created in create().

Parameter

error * optional The error with which the promise rejected. Defined only if the promise is rejected.

ResolveCallback(value)

A function that will resolve the promise created in create().

Parameter

value *|Promise<*> optional The value with which the promise resolved. Defined only if the promise is fulfilled.