Unexpected behavior from JSON.stringify causing it to not return the desired objects

Question

Unexpected behavior from JSON.stringify causing it to not return the desired objects

I have been experimenting with Node.js and Websockets lately. Making progress, but I encountered an unusual issue with JSON.stringify (client side).

I use JSON.stringify to see which object properties the server is returning.

For instance, this is the code snippet I have:

ws.onmessage = function(param1) {
    alert(JSON.stringify(param1));
}

An alert box showing {"isTrusted" : true} pops up.

Seeing this output made me think that the server did not send a message back to the client. To check, I modified the alert function to simply show

alert(param1.data);

The expected message appeared! So, my question is why didn't JSON.stringify display the data object even though it was clearly there?

javascript json websocket

Answer 1

Answer №1

JSON.stringify specifically includes only the own, enumerable properties of an object in the output. This is detailed in the abstract SerializeJSONObject operation in the specifications. In simpler terms, this means that any inherited properties and non-enumerable properties are excluded from the final output.

Interestingly, in the mentioned scenario, the only own, enumerable property found in the message was isTrusted.

Here's an illustrative example:

function Thingy(name, age) {
  // Set `name` as an own, enumerable property
  this.name = name;
  
  // Set `age` as an own, non-enumerable property
  Object.defineProperty(this, "age", {
    value: age
  });
}

// Establish `what` as a property that all `Thingy` instances will inherit:
Thingy.prototype.what = "evs";

// Create an instance
var t = new Thingy("foo", 42);

// Retrieve the JSON representation:
console.log(JSON.stringify(t)); // {"name":"foo"}

The key lesson to learn from this is that traditional alert-style debugging is becoming outdated in the current landscape. Instead of fumbling around blindly with alerts (or console.log), it's more effective to utilize the robust debugger integrated into your web browser. Set a breakpoint at the start of your function, and once it's triggered, view the properties of param1 in real-time. This method provides a comprehensive view of both own and inherited properties, enumerable and non-enumerable, along with their current values while your JavaScript execution is paused.

Answer 2

JSON.stringify specifically includes only the own, enumerable properties of an object in the output. This is detailed in the abstract SerializeJSONObject operation in the specifications. In simpler terms, this means that any inherited properties and non-enumerable properties are excluded from the final output.

Interestingly, in the mentioned scenario, the only own, enumerable property found in the message was isTrusted.

Here's an illustrative example:

function Thingy(name, age) {
  // Set `name` as an own, enumerable property
  this.name = name;
  
  // Set `age` as an own, non-enumerable property
  Object.defineProperty(this, "age", {
    value: age
  });
}

// Establish `what` as a property that all `Thingy` instances will inherit:
Thingy.prototype.what = "evs";

// Create an instance
var t = new Thingy("foo", 42);

// Retrieve the JSON representation:
console.log(JSON.stringify(t)); // {"name":"foo"}

The key lesson to learn from this is that traditional alert-style debugging is becoming outdated in the current landscape. Instead of fumbling around blindly with alerts (or console.log), it's more effective to utilize the robust debugger integrated into your web browser. Set a breakpoint at the start of your function, and once it's triggered, view the properties of param1 in real-time. This method provides a comprehensive view of both own and inherited properties, enumerable and non-enumerable, along with their current values while your JavaScript execution is paused.

Unexpected behavior from JSON.stringify causing it to not return the desired objects

Answer №1

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