How to use jQuery to send JSON data to a Grails app

This took me a while to figure out, so here it is for anyone else who’d like to know. Firstly, I was quite surprised to learn that jQuery doesn’t have a built in method for turning objects into JSON, so you’ll need the JSON parser/creator from json.org. Then you can write your javascript POST function using the jQuery ajax method. Here I’ve left the content type as text/plain, which is not strictly correct but works with the Groovy code.

function postTreeData(){
    $.ajax({
        type: "POST",
        url: "savedata",
        contentType : "text/plain",
        dataType: 'json',
        data: JSON ...
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