javascript - PHP 'array() image' equivalent for javascript

Question

I am trying to upload image to an Etsy listing via their API v2. Their documentation have code example of image upload in PHP, in which the POST request body parameter is given like this

$params = array('@image' => '@'.$source_file.';type='.$mimetype);

How would I go about replicating this in JavaScript? I have tried sending the image blob as the image parameter but it does not seem to be working.

Edit: I am using npm oauth package. Here is my complete code that I am using to call the API.

var oauth1 = new OAuth1.OAuth(
        'https://openapi.etsy.com/v2/oauth/request_token?scope=email_r%20listings_r%20listings_w%20listings_d',
        'https://openapi.etsy.com/v2/oauth/access_token',
        'api_key',
        'api_secret',
        '1.0A',
        null,
        'HMAC-SHA1'
      );
    oauth1.post(
    'https://openapi.etsy.com/v2/listings/915677000/images',
    req.user.etsy.oauth_token,
    req.user.etsy.oauth_token_secret,
    {
        'listing_id': 915677000,
        'image': <image has to go here>
    },
    'multipart/form-data',           
    function (e, data, response){
        if (e) console.error(e);
        // let body = JSON.parse(data);
        console.log(data);
        res.redirect('/create-listings')
    });