js: fetch with non-utf-8 response

js_fetch_non-utf-8_response.js

function transformWindows1251ToUTF8(response) {
	const transformedBody = response.body
		.pipeThrough(new TextDecoderStream("windows-1251"))
		.pipeThrough(new TextEncoderStream("utf-8"));
	return new Response(transformedBody);
}

fetch('https://vk.com/al_im.php', {
	credentials: 'include',
	method: 'POST',
	headers: {
		'content-type': 'application/x-www-form-urlencoded;charset=utf-8',
		'x-requested-with': 'XMLHttpRequest',
		'origin': 'https://vk.com'
	},
	body: '_smt=im%3A2&act=a_dialogs_preload&al=1&gid=0&im_v=2&rs='
}).then(transformWindows1251ToUTF8).then(resp=>resp.json()).then(console.log)