Collection

// Removes a layer from the map using Collection.remove();
map.layers.remove(layer);

// a collection of graphics displayed in the view
const graphics = view.graphics;

for (const graphic of graphics){
  // do something with each view graphic
}

// reactiveUtils watch method can be used to watch the visible
// property of each layer within the map.allLayer's collection
const handle = reactiveUtils.watch(
  () => view.map.allLayers.every((layer) => layer.visible),
  (allVisible) => {
    console.log(`All layers are visible = ${allVisible}`);
  }
);

Property Overview

Property Details

declaredClass Stringreadonly inherited

Since: ArcGIS Maps SDK for JavaScript 4.7

The name of the class. The declared class name is formatted as esri.folder.className.

length Number

The number of items in the Collection.

Method Overview

Method Details

add(item, index)

Adds a single item to the collection. The change event is fired after an item is added to the Collection.

Parameters

item * The item to add.

index Number optional Zero-based index of where in the collection to add the item. If not specified, the items will be added at the end.

Example

let gpc = new Graphic();  // Creates a new graphic
let layer = new GraphicsLayer(); // Creates a new graphics layer
layer.graphics.add(gpc);  // Adds graphic to layer's graphics collection

addHandles(handleOrHandles, groupKey)inherited

Since: ArcGIS Maps SDK for JavaScript 4.25

Adds one or more handles which are to be tied to the lifecycle of the object. The handles will be removed when the object is destroyed.

// Manually manage handles
const handle = reactiveUtils.when(
  () => !view.updating,
  () => {
    wkidSelect.disabled = false;
  },
  { once: true }
);

this.addHandles(handle);

// Destroy the object
this.destroy();

Parameters

handleOrHandles WatchHandle|WatchHandle[] Handles marked for removal once the object is destroyed.

groupKey * optional Key identifying the group to which the handles should be added. All the handles in the group can later be removed with Accessor.removeHandles(). If no key is provided the handles are added to a default group.

addMany(items, index)

Adds multiple items to the collection. The change event is fired after items are added to the Collection.

Parameters

items Array|Collection An array or collection of items to add.

index Number optional Zero-based index of where in the collection to add the items. If not specified, the items will be added at the end.

Example

// Creates two new graphics
let gpc1 = new Graphic();
let gpc2 = new Graphic();

let layer = new GraphicsLayer(); // Creates a new graphics layer

// Adds both graphics to layer's graphics collection
layer.graphics.addMany([gpc1, gpc2]);

at(index){*}

Since: ArcGIS Maps SDK for JavaScript 4.23

Returns the item at the specified index, allowing for positive and negative integers. Negative integers count back from the last item in the array.

Parameter

index Number Index of the item in the Collection to retrieve. It can be a relative index from the end of the Collection.

Returns

Type	Description
*	The item in the Collection stored at the specified index.

See also

• Array.prototype.at()

Example

// get the layer at the first position
let firstLayer = map.layers.at(0);
// get the layer at the last position
let lastLayer = map.layers.at(-1);

clone(){Collection}

Creates a deep clone of the Collection. To create a shallow clone of the collection, use slice().

Returns

Type	Description
Collection	A clone of the Collection that invoked this method.

See also

• slice()

Example

// slides is a clone of the scene slides
let slides = scene.presentation.slides.clone();

concat(value){Collection}

Creates a new Collection containing the items in the original Collection joined with the items in the input array or Collection.

Parameter

value Array|Collection The array or Collection to append to the existing Collection.

Returns

Type	Description
Collection	A new Collection comprised of the items in the Collection that invoked this method combined with the input items.

See also

• Array.prototype.concat()

Example

// creating a collection of all the basemap's layers.
let basemap = map.basemap;
let basemapLayers = basemap.baseLayers.concat(basemap.referenceLayers);

emit(type, event){Boolean}

Since: ArcGIS Maps SDK for JavaScript 4.5

Emits an event on the instance. This method should only be used when creating subclasses of this class.

Parameters

type String The name of the event.

event Object optional The event payload.

Returns

Type	Description
Boolean	true if a listener was notified

every(callback){Boolean}

Determines whether all items in the Collection pass a test defined by callback. Each item in the Collection is passed into the callback until one returns a value of false.

Parameter

callback ItemTestCallback The function to call for each item in the Collection.

Returns

Type	Description
Boolean	Returns true if every call to the callback function returned true. Returns false if at least one call to the callback returned false.

See also

• Array.prototype.every()

Example

let meetsStandardSize = graphicsLayer.graphics.every(function(item, i){
  // Tests each geometry's area to see if it is greater than 1,000 acres
  return calculateArea(item.geometry) > 1000;
});

filter(callback){Collection}

Filters the Collection's items based on a test defined by the callback function. Each item is passed into the callback function, which returns true if the item passes the test and false if it does not.

Parameter

callback ItemTestCallback The function that defines a test for determining whether to return the item in a new Collection.

Returns

Type	Description
Collection	Returns a new Collection containing the items that passed the filter test.

See also

• Array.prototype.filter()

Example

// filteredLayers is a Collection of all the non-visible layers in the map
let filteredLayers = map.layers.filter(function(layer){
  return !layer.visible;
});

find(callback){*}

Returns an item in the Collection if that item passes a test as defined in the callback function. Each item is passed into the callback function, which returns true if the item passes the test and false if it does not.

Parameter

callback ItemTestCallback The testing function that will assess each item in the Collection. Returns true if an item passes the test and false if it fails.

Returns

Type	Description
*	The first item in the Collection that satisfies the test function.

See also

• Array.prototype.find()

Example

// If the id of a map layer is already known, get the layer that matches the id
let myLayer = map.layers.find(function(layer){
  return layer.id === "speciesLyr01";
});
// myLayer references the layer in map with ID "speciesLyr01"

findIndex(callback){Number}

Returns the index of an item in the Collection if that item passes a test as defined in the callback function. Each item is passed into the callback function, which returns true if the item passes the test and false if it does not.

Parameter

callback ItemTestCallback The testing function that will assess each item in the Collection. Returns true if an item passes the test and false if it fails.

Returns

Type	Description
Number	Returns the index of the Collection item that satsifies the test function. If an item fails the test, -1 is returned.

See also

• Array.prototype.findIndex()

Example

// gpcIndex is assigned the index of the first graphic whose name
// property is 'Redlands'. This result can be used in getItemAt()
let gpcIndex = graphicsLyr.graphics.findIndex(function(item){
  return item.attributes.name === "Redlands";
});

flatten(callback){Collection}

Flattens a hierarchical Collection containing at least one child collection. Each item in the collection is passed into the callback function, which should check for child collections specified by the developer. A flat collection of all items (parent and children) is returned.

This is useful for scenarios where the user would like to search all the layers in a map, including a GroupLayer's layers and a MapImageLayer's sublayers. The callback should return the sub-collection of the item. If multiple levels of collections exist in the hierarchy, then this method recursively executes for all sub-collections.

Parameter

callback ItemCallback A function that will assess each item in the Collection.

Returns

Type	Description
Collection	Returns a flat collection of all items in the original collection and their children.

Example

// create a MapImageLayer with several sublayers and add to a map
// containing another GraphicsLayer
let layer = new MapImageLayer({ sublayers: [ ... ] });
let map = new Map({
  layers: [ layer, new GraphicsLayer() ]
});

// A flat collection of all layers and sublayers
// (if layer is a MapImageLayer) in the map.
// This collection may be searched or used for other purposes
let allLayersAndSublayers = map.layers.flatten(function(item){
  return item.layers || item.sublayers;
});

forEach(callback)

Executes the input function for each item in the Collection.

Parameter

callback ItemCallback The function to call for each item in the Collection.

See also

• Array.prototype.forEach()

Example

graphicsLayer.graphics.forEach(function(item, i){
  // Do something here to each graphic like calculate area of its geometry
  calculateArea(item.geometry);
});

getItemAt(index){*}

Returns the item at the specified index.

Parameter

index Number Zero-based index of the item in the Collection to retrieve.

Returns

Type	Description
*	The item in the Collection stored at the specified index.

Example

// Assigns the base layer at index 0 to baseLayer
let baseLayer = map.basemap.baseLayers.getItemAt(0);

hasEventListener(type){Boolean}

Indicates whether there is an event listener on the instance that matches the provided event name.

Parameter

type String The name of the event.

Returns

Type	Description
Boolean	Returns true if the class supports the input event.

hasHandles(groupKey){Boolean}inherited

Since: ArcGIS Maps SDK for JavaScript 4.25

Returns true if a named group of handles exist.

Parameter

groupKey * optional A group key.

Returns

Type	Description
Boolean	Returns true if a named group of handles exist.

Example

// Remove a named group of handles if they exist.
if (obj.hasHandles("watch-view-updates")) {
  obj.removeHandles("watch-view-updates");
}

includes(searchElement){Boolean}

Tests if an item is present in the new Collection.

Parameter

searchElement * The item to search for in the collection.

Returns

Type	Description
Boolean	true if the item is in the collection.

See also

• Array.prototype.includes()

Example

// check if a layer is in the map's operational layers.
if (view.map.layers.includes(myLayer)) {
  // ...
}

indexOf(searchElement, fromIndex){Number}

Returns the index of an element in the collection.

Parameters

searchElement * Item to search for in the collection.

fromIndex Number optional Use if you don't want to search the whole collection or you don't want to search from the start.

Returns

Type	Description
Number	The location of the first match found in the collection, or -1 if there is no match.

See also

• Array.prototype.indexOf()

Example

// index is the index of the first graphic in the
// graphics layer that matches the input graphic
let index = graphicsLayer.graphics.indexOf(graphic);

isCollection(value){Boolean}static

Determines whether the passed value is a Collection.

Parameter

value * The value to be checked.

Returns

Type	Description
Boolean	true if the test passes, false otherwise.

join(separator){String}

Creates a string representation of the items in the Collection.

Parameter

separator String optional Default Value: , The separator used between each item in the final string.

Returns

Type	Description
String	The string representation of the items.

See also

• Array.prototype.join()

Example

let stringCollection = new Collection(["how", "are", "you", "doing?"]);
let phrase = stringCollection.join(" ");

// Prints "how are you doing?"
console.log(phrase);

lastIndexOf(searchElement, fromIndex){Number}

Returns the last index of an element in the collection.

Parameters

searchElement * Item to search for in the collection.

fromIndex Number optional Use if you don't want to search the whole collection, or you don't want to search from the end.

Returns

Type	Description
Number	The location of the last match found in the collection, or -1 if there is no match.

See also

• Array.prototype.lastIndexOf()

Example

// index is the index of the first graphic in the
// graphics layer that matches the input graphic
let index = graphicsLayer.graphics.lastIndexOf(graphic);

map(callback){Collection}

Passes each Collection item into the callback function and returns a new array of the returned values. For example, if you have a Collection of numbers and would like to add each number by 10, you can use map() to create a new Collection with the same numbers incremented by 10.

Parameter

callback ItemMapCallback The function that processes each item in the Collection and returns a new value at the same index of the original item.

Returns

Type	Description
Collection	Returns a new collection containing the new items generated from the callback.

See also

• Array.prototype.map()

Example

// Gets the geometries of the graphics and assigns them to a new Collection
let geoms = graphicsLayer.graphics.map(function(item, i){
  return item.geometry;
});

ofType(type){Object}static

Creates a subclass of Collection containing a typed object.

Parameter

type Object The type to assign the Collection.

Returns

Type	Description
Object	The typed collection.

Example

require(["esri/core/Collection", "esri/geometry/Point"],
  function(Collection, Point){
    let PointCollection = Collection.ofType(Point);
    let collection = new PointCollection();
    collection.add([-100,40]);
    let point = collection.getItemAt(0);
    // point.x = -100; point.y = 40
});

on(type, listener){Object}

Registers an event handler on the instance. Call this method to hook an event with a listener.

Parameters

type String|String[] An event or an array of events to listen for.

listener Function The function to call when the event fires.

Returns

Type	Description
Object	Returns an event handler with a remove() method that should be called to stop listening for the event(s). Property Type Description remove Function When called, removes the listener from the event.

Example

view.on("click", function(event){
  // event is the event handle returned after the event fires.
  console.log(event.mapPoint);
});

pop(){*}

Removes the last item from the collection and returns it.

Returns

Type	Description
*	The last item in the collection.

See also

• Array.prototype.pop()

Example

// Removes the last layer in the map and stores it in lastLayer
let lastLayer = map.layers.pop();

push(item){Number}

Adds an item(s) to the end of the collection.

Parameter

item * An item or comma-separated list of items to add to the end of the collection.

Returns

Type	Description
Number	The new length of the collection.

See also

• Array.prototype.push()

Examples

// Adds a new graphic to the end of the graphics collection on a GraphicsLayer
graphicsLyr.graphics.push(newGraphic);

// Adds three new graphics to the end of the GraphicsLayer's graphics collection
graphicsLyr.graphics.push(g1, g2, g3);

reduce(callback){*}

Reduces all items in the collection (from left to right) into a single variable using callback.

Parameter

callback ItemReduceCallback The function that processes each item in the Collection and appends it to the previous item.

Returns

Type	Description
*	Returns the value representing the reduction of the Collection's items.

See also

• Array.prototype.reduce()

• reduceRight

reduceRight(callback, initialValue){*}

Reduces all items in the collection (from right to left) into a single variable using callback.

Parameters

callback ItemReduceCallback The function that processes each item in the Collection and appends it to the previous item.

initialValue * optional Item to use as the first element to process in callback.

Returns

Type	Description
*	Returns the value representing the reduction of the Collection's items.

See also

• Array.prototype.reduceRight()

• reduce

remove(item)

Removes an item from the collection. The change event is fired after an item is removed from the Collection.

Parameter

item * The item to remove.

Example

let layer = map.layers.getItemAt(4);
// Removes the fifth layer from the map
map.layers.remove(layer);

removeAll()

Removes all items from the collection.

Example

// Removes all layers from the map
map.layers.removeAll();

removeAt(index){*}

Removes an item from the collection at a specified index. The change event is fired after an item is removed from the Collection.

Parameter

index Number The index of the item to remove..

Returns

Type	Description
*	The removed item if present in the collection, undefined otherwise.

Example

// Removes the layer at index 4 of the map
map.layers.removeAt(4);

removeHandles(groupKey)inherited

Since: ArcGIS Maps SDK for JavaScript 4.25

Removes a group of handles owned by the object.

Parameter

groupKey * optional A group key or an array or collection of group keys to remove.

Example

obj.removeHandles(); // removes handles from default group

obj.removeHandles("handle-group");
obj.removeHandles("other-handle-group");

removeMany(items){*}

Removes each item in the input array. If an item is present multiple times in the collection, only the first occurrence is removed. The change event is fired after an item is removed from the Collection.

Parameter

items Array|Collection The items to remove.

Returns

Type	Description
*	The removed items present in the collection.

Example

let refLayers = [refLyr1, refLyr2, refLyr3];
// Removes three reference layers in the refLayers
// collection from the basemap's referenceLayers
map.basemap.referenceLayers.removeMany(refLayers);

reorder(item, index){*}

Moves an item in the Collection to a specified index. The change event is fired after an item is moved in the Collection.

Parameters

item * The item to move.

index Number The index to move the item to.

Returns

Type	Description
*	The item that was moved. undefined if item is not in the collection

Example

// Get the first two layers in a map
let layer1 = map.layers.getItemAt(0);
let layer2 = map.layers.getItemAt(1);

// Moves the second layer to the first position in the map.layers Collection
// effectively swapping the positions of layer1 and layer2
map.layers.reorder(layer2, 0);

reverse(){Collection}

Reverses the collection in place.

Returns

Type	Description
Collection	The reversed collection.

See also

• Array.prototype.reverse()

Example

// Reverse layers from the map
map.layers.reverse();

shift(){*}

Removes the first item from the collection (at index 0), and returns it. The remaining items of the collection are then shifted down one index from their previous location.

Returns

Type	Description
*	The first item in the collection.

See also

• Array.prototype.shift()

Example

// Removes the first layer in the map and stores it in firstLyr
let firstLyr = map.layers.shift();

slice(begin, end){Collection}

Creates a new Collection comprised of a portion of the original Collection.

Parameters

begin Number optional The index of the first item to extract.

end Number optional The index of the last item to extract.

Returns

Type	Description
Collection	Returns a new Collection containing the items in the specified range.

See also

• Array.prototype.slice()

Example

// get the graphics from index 50 to 100;
let selection = graphicsLayer.graphics.slice(50, 100);

some(callback){Boolean}

Determines whether an item in the Collection passes a test defined by callback. Each item in the Collection is passed into the callback until one returns a value of true.

Parameter

callback ItemCallback The function that defines the test for each Collection item.

Returns

Type	Description
Boolean	Returns true if any of the items in the Collection pass the test defined in callback. Returns false if all items fail the test.

See also

• Array.prototype.some()

Example

// If at least one of the point graphics has a geometry whose
// elevation is above 1000m, then passes will have a value of true.
// Otherwise, it will be false.
let passes = graphicsLayer.graphics.some(function(item, i){
  return item.geometry.z > 1000;
});

sort(compareFunction)

Sorts the Collection in place.

Parameter

compareFunction ItemCompareCallback optional The function that defines a comparison of two items in the collection.

See also

• Array.prototype.sort()

Example

// Sort graphics based on their elevation or z-value
let sortedGraphics = graphicsLayer.graphics.sort(function(a, b){
  if(a.geometry.z > b.geometry.z){
    return 1;
  }
  else if (a.geometry.z < b.geometry.z){
    return -1;
  }
  else {
    return 0;
  }
});

splice(start, deleteCount, items){Array}

Removes existing items and/or adds new items to the collection.

Parameters

start Number Index at which to start changing the collection.

deleteCount Number Indicates the number of collection items to remove. If 0 is used then no elements are removed and at least one new item should be added in the items parameter.

items * The item or comma-separated list of items to add to the collection.

Returns

Type	Description
Array	An array of the deleted items formerly part of the collection.

See also

• Array.prototype.splice()

Examples

// map.layers is a collection of 6 layers
// Adds a seventh layer to the map at index 3
map.layers.splice(3, 0, layer7);

// Removes two layers starting from index 2 and adds the
// specified layers in the positions of the former layers
let oldLayers = map.layers.splice(2, 2, layer8, layer9, layer10);

// oldLayers = [layer2, layer3]

toArray(){Array}

Returns a new array object containing the Collection's items.

Returns

Type	Description
Array	An array containing the Collection's items.

Example

// Creates an array populated with the map's layers
let mapLayersArray = map.layers.toArray();

unshift(items){Number}

Adds one or more items to the beginning of the collection.

Parameter

items * The item(s) to add to the beginning of the collection.

Returns

Type	Description
Number	The new length of the collection.

See also

• Array.prototype.unshift()

Example

// If a map's basemap has 3 baseLayers: baseLyr0, baseLyr1, baseLyr2
map.basemap.baseLayers.unshift(baseLyr3);

// Now the baseLayers collection is: baseLyr3, baseLyr0, baseLyr1, baseLyr2

Type Definitions

ItemCallback(item, index)

The function that is called for each Collection item.

Parameters

item * The current item being assessed in the collection.

index Number The index of the item being assessed.

ItemCompareCallback(firstItem, secondItem){Number}

The function that defines a comparison.

Parameters

firstItem * the first item in the comparison.

secondItem * the second item in the comparison.

Returns

Type	Description
Number	-1 if firstItem is smaller than secondItem, 1 if it is larger, and 0 if both are equal.

ItemMapCallback(item, index){*}

The function that defines a mapping and is called for each Collection item.

Parameters

item * The current item being assessed in the collection.

index Number The index of the item being assessed.

Returns

Type	Description
*	the new value that replaces item.

ItemReduceCallback(previousValue, currentValue, index){*}

The function that defines a reducer.

Parameters

previousValue * The item previously reduced value.

currentValue * The current item being assessed in the collection.

index Number The index of the item being assessed.

Returns

Type	Description
*	the value to be passed to the next reducer.

ItemTestCallback(item, index){Boolean}

The function that defines a test and is called for each Collection item.

Parameters

item * The current item being assessed in the collection.

index Number The index of the item being assessed.

Returns

Type	Description
Boolean	true if the test passes, false otherwise.

Event Overview

Event Details

after-add

Fires after an item has been added to the collection.

Property

item * The item added to the collection.

Example

// indicates a layer has been added to the map
map.layers.on("after-add", function(event){
  console.log(event.item, " has been added to the map.");
});

after-changes

Fires after an item has been added, reordered or removed from the collection.

Example

map.layers.on("after-changes", function(event){
  console.log(event, " layer was added/removed from the map.");
});

after-remove

Fires after an item has been removed from the collection.

Property

item * The item to remove from the collection.

Example

// indicates a layer has been removed from the map
map.layers.on("after-remove", function(event){
  console.log(event.item, " has been removed from the map.");
});

before-add

Fires before an item is added to the collection. This event can be used to prevent an item from being added to the collection by cancelling it with the event.preventDefault() method.

Properties

cancellable Boolean Indicates if the change event can be cancelled.

defaultPrevented Boolean Indicates if this event has previously been cancelled by another event handler.

item * The item to add to the collection.

preventDefault Function A method that prevents the item from being added to the collection.

Example

// prevents a layer from being added to the map more than once.
map.layers.on("before-add", function(event){
   if(map.layers.includes(event.item)){
     event.preventDefault();
     console.log("layer already exists in map.");
   }
});

before-changes

Fires before any modifications are performed on the collection. This event can be used to prevent an item from being added or removed from the collection by cancelling it with the event.preventDefault() method.

Properties

cancellable Boolean Indicates if the change event can be cancelled.

defaultPrevented Boolean Indicates if this event has previously been cancelled by another event handler.

item * The item to add or remove from the collection.

preventDefault Function A method that prevents the item from being added or removed from the collection.

Example

map.layers.on("before-changes", function(event){
  // prevents layers from being added/removed from the map
  event.preventDefault();
});

before-remove

Fires before an item has been removed from the collection. This event can be used to prevent an item from being removed from the collection by cancelling it with the event.preventDefault() method.

Properties

cancellable Boolean Indicates if the change event can be cancelled.

defaultPrevented Boolean Indicates if this event has previously been cancelled by another event handler.

item * The item to remove from the collection.

preventDefault Function A method that prevents the item from being removed from the collection.

Example

// prevents a layer from being removed from the basemap
map.basemap.baseLayers.on("before-remove", function(event){
   if(map.basemap.baseLayers.includes(event.item)){
     event.preventDefault();
     console.log("layer cannot be removed from basemap.");
   }
});

change

Fires after an item has been added, reordered, or removed from the Collection. Using methods of other classes that affect properties of type Collection will also cause this event to fire, such as Map.add(), Map.remove(), Map.reorder().

For example, map.layers.add(newLyr) and map.add(newLyr) which uses Map.add() to add a new layer to the map.layers collection will cause this event to fire.

The change event can be used to notify the developer/user of changes to the collection.

Properties

added Array An array of items added to the collection using either add() or addMany().

moved Array An array of items that moved in the collection using reorder().

removed Array An array of items removed from the collection using either remove(), removeMany(), removeAt(), or removeAll().

Example

// This function will fire each time a layer is either added,
// moved, or removed from the map.layers Collection
map.layers.on("change", function(event){
  let newLayers = event.added; // An array of layers added to the map.layers Collection
  let reorderedLayers = event.moved;  // An array of layers moved in the Collection
  let removedLayers = event.removed;  // An array of layers removed from map
});