Complex objects in javascript

Question

I'm fiddling around with a library called bcoin for node. Running the following code:

  chain.on('block', function(block) {
    console.log('Connected block to blockchain:');
    block.txs.forEach(function(t) {
      t.inputs.forEach(function(i) {
        console.log(typeof i, i);
        console.log(JSON.stringify(i));
      });
    });
  });

This is the response I'm getting:

Connected block to blockchain:
object { type: 'coinbase',
  subtype: null,
  address: null,
  script: <Script: 486604799 676>,
  witness: <Witness: >,
  redeem: null,
  sequence: 4294967295,
  prevout: <Outpoint: 0000000000000000000000000000000000000000000000000000000000000000/4294967295>,
  coin: null }
{"prevout":{"hash":"0000000000000000000000000000000000000000000000000000000000000000","index":4294967295},"script":"04ffff001d02a402","witness":"00","sequence":4294967295,"address":null}

Notice that even though the attribute type for example, is shown when we print i, that attribute does not exist when we JSON.stringify the object. If I tried to console.log(i.type) I'd get undefined.

How is that possible? And what is a good way of debugging what's going on with an object?

You your inner most function add: if ( i ) {, that will take care of i being null or undefined. — SPlatten
– SPlatten, Commented Oct 24, 2017 at 6:49
I'm trying to understand why it's undefined in the first place. — Or Weinberger
– Or Weinberger, Commented Oct 24, 2017 at 6:51
then expand your logic and be more verbose, test 't' before looping — SPlatten
– SPlatten, Commented Oct 24, 2017 at 6:52

Rajesh Dixit · Accepted Answer · 2017-10-24 06:57:55Z

1

JSON.stringify will only includes enumerable properties that are not functions.

So if you define a property and set as non-enumerable, it will not be a part of JSON string.

var obj = {
  a: 'test'
};

// Non-enumerable property
Object.defineProperty(obj, 'type', {
  enumerable: false,
  value: 'Test'
});

// Get property
Object.defineProperty(obj, 'type2', {
  get: function(){
    return 'Test 2'
  }
});


console.log(JSON.stringify(obj), obj);
console.log(obj.type, obj.type2)

edited Oct 24, 2017 at 6:57

answered Oct 24, 2017 at 6:44

Rajesh Dixit

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4 Comments

Or Weinberger Over a year ago

Interesting. Why are you able to access obj.type while I cannot access i.type?

Or Weinberger Over a year ago

This is a node application, so it's not running inside the browser. Regarding the object not being the same, the code above is what I'm running, not sure how it is possible for it to be mutated in the way I'm running it.

Or Weinberger Over a year ago

Although this is interesting, it doesn't answer the question.

Rajesh Dixit Over a year ago

@OrWeinberger Thanks for responding. Also, as I previously stated, type is not the only property missing. My suggestion, you should check if any you are overriding an internal function. This might be done my some library. This is because, <Script: 486604799 676> is not a valid value in JS Object. So there is some mechanism that is either printing the values in special way or removing values in stringify

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