Post Map as JSON using JSweet

Question

I'd like to send a java.util.HashMap converted to JSON from the client to the server.

I'm using JSweet to transpile Java to JavaScript for the client side.

I had a look at XMLHttpRequest and tried to prepare the map for transfer using JSON.stringify(new HashMap<>()) but this resulted in a

TypeError: cyclic object value

on the client side.

These are my relevant dependencies (using Gradle):

// Java to JavaScript transpilation 
compile "org.jsweet:jsweet-transpiler:1.2.0-SNAPSHOT"
compile "org.jsweet.candies:jsweet-core:1.1.1"
// Allows us to use Java features like Optional or Collections in client code
compile "org.jsweet.candies:j4ts:0.2.0-SNAPSHOT"

Answer 1

I had to convert the java.util.Map to a jsweet.lang.Object before encoding it as JSON using stringify.

Here's the code to send a java.util.Map as JSON to the server using JSweet:

void postJson(Map<String, String> map, String url) {
    XMLHttpRequest request = new XMLHttpRequest();

    // Post asynchronously
    request.open("POST", url, true);
    request.setRequestHeader("Content-Type", "application/json;charset=UTF-8");

    // Encode the data as JSON before sending
    String mapAsJson = JSON.stringify(toJsObject(map));
    request.send(mapAsJson);
}

jsweet.lang.Object toJsObject(Map<String, String> map) {
    jsweet.lang.Object jsObject = new jsweet.lang.Object();

    // Put the keys and values from the map into the object
    for (Entry<String, String> keyVal : map.entrySet()) {
        jsObject.$set(keyVal.getKey(), keyVal.getValue());
    }
    return jsObject;
}

Use it like this:

Map<String, String> message = new HashMap<>();
message.put("content", "client says hi");
postJson(message, "http://myServer:8080/newMessage");