How to pass json POST data to Web API method as an object?

web-development

ajax

json-stringify

api-endpoint

byNikita Barsukov·Feb 19, 2025

To efficiently pass JSON data to a Web API method, use JSON.stringify on your JavaScript object to encode it for transmission. In an ASP.NET context, define a model class matching your JSON structure. Include the [FromBody] attribute on the server controller method parameter to parse the incoming JSON into your model instance. The following JavaScript snippet using fetch demonstrates this:

const data = { name: "Jane", age: 28 }; // JSON object working 9 to 5, ready to earn its keep

fetch('api/yourMethod', {
  method: 'POST', // Knock-knock... can POST-man Pat deliver?
  headers: { 'Content-Type': 'application/json' }, // Let's stick a postage stamp labeled 'json' on it
  body: JSON.stringify(data), // Wrap up the package nicely
})
.then(res => res.json())
.then(console.log)
.catch(console.error); // Send console.log() some flowers, console.error() needs some love too

Ensure that data keys align with your server-side model's properties for flawless deserialization.

Headers and ContentType: present your JSON correctly

Defining the correct Content-Type is crucial for ensuring your JSON data can correctly board the plane to API-land. For complex objects, the custom declaration must say application/json. Remember to set this for your fetch or AJAX request headers.

Here are some tips:

Be explicit with contentType, verify that it is set to 'application/json'.
Your JSON string properties should conform to your API endpoint model properties.
Use the [HttpPost] attribute to signify the desired action for your API method.
Verify your API endpoint URL for your AJAX call is correct. As in life and meetings, location matters.

Soldiering through complex objects

Handling complex objects doesn't have to feel like endgame. Here are a few survival tips:

Make sure to JSON.stringify your complex objects.
Include the [FromBody] attribute in your method to correctly bind JSON data to your parameter object.
Controlling the structure of your JSON data against your WebAPI model helps keep a strong-typed API structure and weeds out surprises.

Error-proofing and callback usage

Plan not only for success, but failure too. Here are a few tips:

Handle success and error responses with callbacks to manage AJAX calls' results.
Use try/catch blocks to handle errors when implementing fetch or AJAX calls.
Be clear with users about the success or failure of their API request. The first rule of API Club is "Always talk about your HTTP statuses."

Custom routing and method control

A few tips on ensuring your JSON data doesn't lose its way to the endpoint:

Love your routes: Registering custom action routes in your Web API configuration can save a ton of guesswork.
Actions speak louder: Use attributes like [AcceptVerbs] and [HttpPost] for a granular control over your action methods.

Content type: use wisely

The Content-Type can affect how your data is sent and how it is processed on the server:

JSON.stringify should be used for complex types; for simple types, a specific format is not always necessary.
Remember there are other content types, like multipart/form-data for file uploads. Know which type suits your situation.

explain-codes / Web development / How to pass json POST data to Web API method as an object?

Linked

Creating a JSON response using Django and Python



How to get POSTed JSON in Flask?



Get list of JSON objects with Spring RestTemplate



Angularjs passing data to $http.get request



How to access the request body when POSTing using Node.js and Express?

