https://community.esri.com/people/EPolle_TensingInternational/blog/2019/06/02/aan-de-slag-met-arcgis-javascript-inleiding
Watch
Het is mogelijk om met de ArcGIS API for JavaScript te reageren op een verandering in de eigenschap van een instance. Dit kun je doen door dergelijke wijzigingen bij te houden (of te bewaken) met de watch() method.
In het voorbeeld hieronder houden we op deze manier de schaal van de view in de gaten. Dit doen wij in dit voorbeeld om te bepalen welke basiskaart getoond moet worden. Op verzoek van de eindgebruikers tonen we bij een kleine schaal een rustige basiskaart (Topo RD van Esri Nederland), terwijl we op grote schaal een basiskaart met meer detail laten zien (Open Topo van Jan-Willem van Aalst, die ook door Esri Nederland wordt aangeboden). De grens voor het wisselen van de basiskaart is gelegd bij schaal 1:20.000.
Dus elke keer als de gebruiker in- of uitzoomt wordt de schaal gecheckt, en zodra de schaal groter is dan 1:20:000 wordt de Open Topo basiskaart getoond. (Let op: scale geeft het schaalgetal terug, en hoe groter het schaalgetal, hoe kleiner de schaal! Dus zodra het schaalgetal groter is dan 20.000 wordt de Topo RD basiskaart getoond.)
De volledige code staat hieronder en hier kun je het voorbeeld in actie zien.
<SPAN class="doctype token"><!DOCTYPE html></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>html</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>head</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>meta</SPAN> <SPAN class="attr-name token">charset</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>utf-8<SPAN class="punctuation token">"</SPAN></SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>meta</SPAN> <SPAN class="attr-name token">name</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>viewport<SPAN class="punctuation token">"</SPAN></SPAN> <SPAN class="attr-name token">content</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>initial-scale<SPAN class="punctuation token">=</SPAN>1, maximum-scale<SPAN class="punctuation token">=</SPAN>1, user-scalable<SPAN class="punctuation token">=</SPAN>no<SPAN class="punctuation token">"</SPAN></SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>title</SPAN><SPAN class="punctuation token">></SPAN></SPAN>Aan de slag met ArcGIS JavaScript - Wijzigingen bijhouden<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>title</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="language-css style token"><SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>style</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="selector token">html, body, #viewDiv</SPAN> <SPAN class="punctuation token">{</SPAN>
<SPAN class="property token">padding</SPAN><SPAN class="punctuation token">:</SPAN> 0<SPAN class="punctuation token">;</SPAN>
<SPAN class="property token">margin</SPAN><SPAN class="punctuation token">:</SPAN> 0<SPAN class="punctuation token">;</SPAN>
<SPAN class="property token">height</SPAN><SPAN class="punctuation token">:</SPAN> 100%<SPAN class="punctuation token">;</SPAN>
<SPAN class="property token">width</SPAN><SPAN class="punctuation token">:</SPAN> 100%<SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>style</SPAN><SPAN class="punctuation token">></SPAN></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>link</SPAN> <SPAN class="attr-name token">rel</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>stylesheet<SPAN class="punctuation token">"</SPAN></SPAN> <SPAN class="attr-name token">href</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>https://js.arcgis.com/4.11/esri/css/main.css<SPAN class="punctuation token">"</SPAN></SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="language-javascript script token"><SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>script</SPAN> <SPAN class="attr-name token">src</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>https://js.arcgis.com/4.11/<SPAN class="punctuation token">"</SPAN></SPAN><SPAN class="punctuation token">></SPAN></SPAN><SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>script</SPAN><SPAN class="punctuation token">></SPAN></SPAN></SPAN>
<SPAN class="language-javascript script token"><SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>script</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token function">require</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">[</SPAN>
<SPAN class="string token">"esri/Map"</SPAN><SPAN class="punctuation token">,</SPAN>
<SPAN class="string token">"esri/Basemap"</SPAN><SPAN class="punctuation token">,</SPAN>
<SPAN class="string token">"esri/geometry/Point"</SPAN><SPAN class="punctuation token">,</SPAN>
<SPAN class="string token">"esri/views/MapView"</SPAN>
<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="keyword token">function</SPAN><SPAN class="punctuation token">(</SPAN>Map<SPAN class="punctuation token">,</SPAN> Basemap<SPAN class="punctuation token">,</SPAN> Point<SPAN class="punctuation token">,</SPAN> MapView<SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
<SPAN class="keyword token">var</SPAN> topo_RD_EsriNL <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">Basemap</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>portalItem<SPAN class="punctuation token">:</SPAN> <SPAN class="punctuation token">{</SPAN>id<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"7aea6fa913a94176a1074edb40690318"</SPAN><SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN> <SPAN class="comment token">//Topo RD</SPAN>
<SPAN class="keyword token">var</SPAN> open_Topo_RD_EsriNL <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">Basemap</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>portalItem<SPAN class="punctuation token">:</SPAN> <SPAN class="punctuation token">{</SPAN>id<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"0698b71eb7cf47898086d072e574ac32"</SPAN><SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN> <SPAN class="comment token">//Open Topo RD</SPAN>
<SPAN class="keyword token">var</SPAN> map <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">Map</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>
basemap<SPAN class="punctuation token">:</SPAN> topo_RD_EsriNL
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> rdOrigin <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">Point</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>
x<SPAN class="punctuation token">:</SPAN> <SPAN class="number token">155000</SPAN><SPAN class="punctuation token">,</SPAN>
y<SPAN class="punctuation token">:</SPAN> <SPAN class="number token">463000</SPAN><SPAN class="punctuation token">,</SPAN>
spatialReference<SPAN class="punctuation token">:</SPAN> <SPAN class="number token">28992</SPAN>
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> view <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">new</SPAN> <SPAN class="token class-name">MapView</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">{</SPAN>
spatialReference<SPAN class="punctuation token">:</SPAN> <SPAN class="number token">28992</SPAN><SPAN class="punctuation token">,</SPAN>
container<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"viewDiv"</SPAN><SPAN class="punctuation token">,</SPAN>
map<SPAN class="punctuation token">:</SPAN> map<SPAN class="punctuation token">,</SPAN>
center<SPAN class="punctuation token">:</SPAN> rdOrigin<SPAN class="punctuation token">,</SPAN>
zoom<SPAN class="punctuation token">:</SPAN> <SPAN class="number token">3</SPAN>
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="comment token">// watch handler: the callback fires each time the scale of the view changes</SPAN>
<SPAN class="keyword token">var</SPAN> handle <SPAN class="operator token">=</SPAN> view<SPAN class="punctuation token">.</SPAN><SPAN class="token function">watch</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">'scale'</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="keyword token">function</SPAN><SPAN class="punctuation token">(</SPAN>newScale<SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
console<SPAN class="punctuation token">.</SPAN><SPAN class="token function">log</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Scale: "</SPAN><SPAN class="punctuation token">,</SPAN> newScale<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
console<SPAN class="punctuation token">.</SPAN><SPAN class="token function">log</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Basemap: "</SPAN><SPAN class="punctuation token">,</SPAN> map<SPAN class="punctuation token">.</SPAN>basemap<SPAN class="punctuation token">.</SPAN>title<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">(</SPAN>newScale <SPAN class="operator token">></SPAN> <SPAN class="number token">20000</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
map<SPAN class="punctuation token">.</SPAN>basemap <SPAN class="operator token">=</SPAN> topo_RD_EsriNL<SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN> <SPAN class="keyword token">else</SPAN> <SPAN class="punctuation token">{</SPAN>
map<SPAN class="punctuation token">.</SPAN>basemap <SPAN class="operator token">=</SPAN> open_Topo_RD_EsriNL<SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN>
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>script</SPAN><SPAN class="punctuation token">></SPAN></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>head</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>body</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"><</SPAN>div</SPAN> <SPAN class="attr-name token">id</SPAN><SPAN class="attr-value token"><SPAN class="punctuation token">=</SPAN><SPAN class="punctuation token">"</SPAN>viewDiv<SPAN class="punctuation token">"</SPAN></SPAN><SPAN class="punctuation token">></SPAN></SPAN><SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>div</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>body</SPAN><SPAN class="punctuation token">></SPAN></SPAN>
<SPAN class="token tag"><SPAN class="token tag"><SPAN class="punctuation token"></</SPAN>html</SPAN><SPAN class="punctuation token">></SPAN></SPAN><SPAN class="line-numbers-rows"><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN></SPAN>
