这里怎么转字符都会乱码 但是用postman请求就没一点儿问题

const requestTask = wx.request({
					url: 'https://ark.cn-beijing.volces.com/api/v3/bots/chat/completions',
					method: 'POST',
					enableChunked: true,
					responseType: "arraybuffer", // 以 ArrayBuffer 格式接收数据
					data: {
						"model": '',
						"messages": [{
							"role": "user",
							"content": "写一个文章"
						}],
						"stream": true,
					},
					header: {
						'content-type': 'application/json',
						'Authorization': 'Bearer xxx'
					},
					success: response => {},
					fail: error => {}

				});
requestTask.onChunkReceived((response) => {
					const arrayBuffer = response.data;
					const uint8Array = new Uint8Array(arrayBuffer);
					const str = new TextDecoder('utf-8').decode(uint8Array);
					console.log('str:',str)	
});