for my below code I want to setup a default toString() method which overrides the inbuilt toString() for this class. But its not working and I get the output "Queue { data: [] }" instead of expected "Hello This is example". I looked at some already discussed similar questions on SO but no help. I also tried on latest version of Chrome and behaviour is same. I have Node 10.13 with Babel 6 (babel-node --presets env,stage-2 queue.js). Looking for some expert opinion here.

class Queue {
  constructor() {
    this.data = [];
  }
  toString() {
    console.log("Hello This is example");
  }
}

const queue1 = new Queue();
console.log(queue1);

for my below code I want to setup a default toString() method which overrides the inbuilt toString() for this class. But its not working and I get the output "Queue { data: [] }" instead of expected "Hello This is example". I looked at some already discussed similar questions on SO but no help. I also tried on latest version of Chrome and behaviour is same. I have Node 10.13 with Babel 6 (babel-node --presets env,stage-2 queue.js). Looking for some expert opinion here.

class Queue {
  constructor() {
    this.data = [];
  }
  toString() {
    console.log("Hello This is example");
  }
}

const queue1 = new Queue();
console.log(queue1);

• javascript
• class
• ecmascript-6

• Thanks Andreas, let str = queue1 + ""; did the trick. I really wonder why console.log() doesnt call it. Now every time I have to console log it, I have to create str before it. – Sumer Commented Jan 2, 2019 at 13:03
• 1 Because a string is more or less useless (imho) when inspecting (logging) an object. – Andreas Commented Jan 2, 2019 at 13:05

2 Answers 2

You have to trigger the call for .toString() explicitly or implicitly

console.log(queue1.toString());
console.log(queue1 + "");
console.log([queue1, queue2].join());

And .toString() has to return the string representation:

toString() { return "..." }

class Queue {
  constructor() {
    this.data = [];
  }
  toString() {
    return "Hello This is example"; // toString has to return the string representation
  }
}

const queue1 = new Queue();
console.log(queue1 + "");

const queue2 = new Queue();
console.log([queue1, queue2].join());

for my below code I want to setup a default toString() method which overrides the inbuilt toString() for this class. But its not working and I get the output "Queue { data: [] }" instead of expected "Hello This is example".

class Queue {
  constructor() {
    this.data = [];
  }
  toString() {
    console.log("Hello This is example");
  }
}

const queue1 = new Queue();
console.log(queue1);

In the above code the toString method doesn't override the class's toString method. Why? Because the class's toString returns a String.

In your code, console.log("Hello This is example"); doesn't return any value. That is the reason you are getting the output: Queue { data: [] }. This is the default output. If you remove the toString method from your Queue class, the statement console.log(queue1); will still print: Queue { data: [] }.

To make the Queue class object's representation as a string value, you need to code something like this:

toString() {
    return "Hello this is an example";
}

To use the toString in your application you can try the code on any of the lines #2 or #3 below, and it will print: "Hello this is an example".

const queue1 = new Queue();
console.log(queue1); // #2
console.log(queue1.toString()); // #3

Also see this link and Object.prototype.toString().