You can use TextDecoder:

try {
  parsedJson = JSON.parse(new TextDecoder().decode(response as ArrayBuffer));
} catch (e) {
  parsedJson = {};
}

In my case the request is waiting for an ArrayBuffer response, but if an error occours on the backend, I get a JSON object containing the error. I check if the response is an error with this code.

The try-catch block is needed because if the ArrayBuffer is not a json, then the JSON.parse() method will throw an error.

As @wOxxOm said, convert it into a string and then parse it.

Note: This will not work for IE (and possibly Edge as well).

// Obviosuly replace this with whatever your array buffer is
const arrayBuffer = new TextEncoder().encode(JSON.stringify({crawlerInfo: "crawler info"}))

const json = JSON.parse(new TextDecoder().decode(arrayBuffer))
console.log(json)

Use the syntax below to switch back to JSON.

let arrayBufferConverted = JSON.parse(
 String.fromCharCode.apply(null, new Uint8Array(res.data))
   )

Edit: As @Paul LeBeau points out, my answer assumes that the response is ASCII encoded.

Basically you just need to decode the ArrayBuffer into a string and use JSON.parse().

var decodedString = String.fromCharCode.apply(null, new Uint8Array(data));
var obj = JSON.parse(decodedString);
var message = obj['message'];

I ran tests in IE11 & Chrome and this works just fine.

I had check your code. But can't get your output

my server code is:

const WebSocketServer = new require('ws');
let webSocketServer; 
const initServer = async() => {
    let port = 8091;
    webSocketServer = new WebSocketServer.Server({ port });
    webSocketServer.binaryType = 'arraybuffer';
    console.log(`Server start on port: ${port}`)
    webSocketServer.on('connection', function(ws) {
        ws.send(
            JSON.stringify({
                "market": "United States",
                "current_price": 645.00000000,
                "highest_price": 887.00000000,
            }),
        )
    });
}

initServer();

and client code is:

<script>
  const ws = new WebSocket("ws://localhost:8091");
  ws.binaryType = 'arraybuffer';
  ws.onmessage = function(message){ 
    console.log(JSON.parse(message.data));
  }
</script>

output is object:

if you read data from json file try this code:

  const readData = (path) => {
    return new Promise((resolve, reject) => {
      fs.readFile(path, 'utf8', function(err, contents) {
        if (!err)  resolve(JSON.parse(contents))
        else reject(Error(`The fail "${path}" is not read`))
      });
    });  
  }

also try this function:

const arrayBufferToString(buf) {
  return String.fromCharCode.apply(null, new Uint16Array(buf));
}