How can I pass data to a service in Axios and ensure the correct content type and boundary are set?

Passing Data to Service in Axios

Problem: You want to attach a "_boundary" to the header of an Axios API call, but the data is not accessible in the Axios service.

Solution: Axios automatically handles content types for certain request body formats, including FormData. Passing a FormData instance as the data argument will set the appropriate Content-Type and mime boundary without manual configuration.

Detailed Explanation:

Automatic Content Type Handling:

When sending a FormData instance, the runtime automatically sets the Content-Type to "multipart/form-data" and includes the correct mime boundary tokens. This behavior ensures that the data is correctly serialized and sent to the server.

Example:

Here's an example of sending a FormData instance with Axios:

<code class="javascript">const form = new FormData();

// Attach files and other fields to the formData instance
form.append('file', fileInput.files[0]);
form.append('foo', 'foo');

axios.post(url, form);</code>

Handling Custom Content Types:

You only need to manually set the Content-Type if you want to send string data in a specific format (e.g., text/xml, application/json).

Example:

<code class="javascript">const data = JSON.stringify({ foo: 'foo', bar: 'bar' });

axios.post(url, data, {
  headers: { 'content-type': 'application/json' },
});</code>

Avoidance of Axios v0.27.1 and v1.0.0 :

These Axios versions have known issues with handling FormData. It's recommended to use alternatives such as the Fetch API, got (for Node.js), or ky (for browsers).

Node.js Considerations:

When using Axios on the Node.js backend, it won't infer Content-Type headers from FormData instances. To address this, you can use a request interceptor or manually merge the headers.

jQuery $.ajax() Method:

By default, $.ajax() sends payloads as "application/x-www-form-urlencoded" and serializes JavaScript data using jQuery.param(). To allow the browser to automatically set the Content-Type, use the following options:

<code class="javascript">$.ajax({
  url,
  method: 'POST',
  data: body,
  contentType: false, // Let the browser figure out the content type
  processData: false, // Don't attempt to serialize data
});</code>

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