<!DOCTYPE htmtl> <html> <head> <meta charset="utf-8" /> <title>Forms</title> </head> <body> <h3>Submit Json</h3> <button onclick="submitJson()">Submit</button> <script> let payload = { timestamp: 12345, kind: "this is a kind", tags: ["tag1", "tag2", "tag3"], }; function submitJson() { fetch("http://localhost:8080/event", { method: "POST", headers: { Accept: "application/json", "Content-Type": "application/json", }, body: JSON.stringify(payload), }) .then(function (res) { return res.json(); }) .then(function (data) { let expected = { ...payload, id: 1, }; console.log("expected: ", expected); console.log("received: ", data); }); } </script> </body> </html>