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Access data (JSON)

Description

This sample shows how to use esriRequest to download content in JSON format. The snippet below uses this method to retrieve earthquake data in GeoJSON format from USGS Earthquakes Hazards Program.

Once the content is loaded we can access and display this information. The dojo.toJson method is used to convert the JavaScript object and its properties and values into simple text. The response is a JavaScript object, you can access its properties using code like this:

console.log("Title: ", response.value.title);
console.log("Description for first item: ", response.value.items[0].description);

"XMLHttpRequest" objects are subject to the browser same origin security policy. This means that when downloading content with this method you need to setup a proxy if the content is from another origin. The proxy acts as an intermediary between the browser and the server that contains the content you want to download. Instructions for installing and configuring a proxy can be found here.

After installing the proxy make sure that it is configured to handle request to the server that contains the content you are downloading. The proxy is not required if the HTML page and the content are hosted on the same web server.

Code

<!DOCTYPE html>
<html>
<head>
  <title>JSON Content</title>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <link rel="stylesheet" href="https://js.arcgis.com/3.28/esri/css/esri.css">
  <style>
    body{
      font-family: "Arial Unicode MS, Arial, sans-serif";
    }
    #content {
      width: 800px; height: 350px; padding: 5px; overflow: auto;
      border: solid 2px #AAAAAA; background-color: #FFFFFF;
      -moz-border-radius: 5px; -webkit-border-radius: 5px; -o-border-radius: 5px; border-radius: 5px;
      -moz-box-shadow: 0 0 0.5em black; -webkit-box-shadow: 0 0 0.5em black; -o-box-shadow: 0 0 0.5em black; box-shadow: 0 0 0.5em black;
    }
    .failure { color: red; }
    #status { font-size: 12px; }
  </style>

  <script src="https://js.arcgis.com/3.28/"></script>
  <script>
    require([
        "dojo/dom",
        "dojo/on",
        "dojo/dom-class",
        "dojo/_base/json",
        "esri/config",
        "esri/request",
        "dojo/domReady!"
      ],
      function(
        dom,
        on,
        domClass,
        dojoJson,
        esriConfig,
        esriRequest
      ) {

        // Use CORS
        esriConfig.defaults.io.corsEnabledServers.push("earthquake.usgs.gov"); // supports CORS

        // Use proxy if the server doesn't support CORS
        // esriConfig.defaults.io.proxyUrl = "/proxy/";  
        
        dom.byId("url").value = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/1.0_day.geojson";

        dom.byId("content").value = "";

        //handle the Go button's click event
        on(dom.byId("submitRequest"), "click", getContent);

        function getContent(){

          var contentDiv = dom.byId("content");
          contentDiv.value = "";
          domClass.remove(contentDiv, "failure");
          dom.byId("status").innerHTML = "Downloading...";

          var requestHandle = esriRequest({
            "url": dom.byId("url").value
          });
          requestHandle.then(requestSucceeded, requestFailed);
        }

        function requestSucceeded(response, io){
          dom.byId("status").innerHTML = "";
          dojoJson.toJsonIndentStr = "  ";
          dom.byId("content").value = dojoJson.toJson(response, true);
        }
        function requestFailed(error, io){

          domClass.add(dom.byId("content"), "failure");
          dom.byId("status").innerHTML = "";

          dojoJson.toJsonIndentStr = " ";
          dom.byId("content").value = dojoJson.toJson(error, true);

        }
    });
  </script>
</head>
<body>
  <p>Download content available in <b>JSON</b> format using esriRequest. </p>
  <p>
    <input type="text" disabled="true" id="url" size="100"/>
    <input id="submitRequest" type="button" value="GO" />
    <span id="status"></span>
  </p>
  <h2>Content</h2>
  <textarea id="content"></textarea>
</body>
</html>
 
          
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