CODEWITHSUNDEEP
javascriptjsonnode.js
Lost Woods
Lost Woods

Reputation: 3

Appending to JSON is causing error

I am trying to append the ID of a setInterval function to a JSON file, but it gets me an error TypeError: Converting circular structure to JSON

My code looks like this

var clearID = setInterval(function(){
   //do stuff
},(60)*1000);

fs.readFile('path', 'utf8', function readFileCallback(err, data){
   if (err) return console.log(err);   
     var doc = JSON.parse(data);
     doc.IDs.shift();
     doc.IDs.push(clearID);
     var saved = JSON.stringify(doc);
  fs.writeFile('path', saved, 'utf8', (err)=>{
    if(err) return console.log(err);
  });
});

What should I change to stop this error?

Upvotes: 0

Views: 93

Answers (1)

Adam Jenkins
Adam Jenkins

Reputation: 55792

In a NodeJS environment, you simply can't convert the return value of a setInterval call to JSON string. The error you get is very clear, the return value contains one or more circular references.

Try this (in a node environment):

var x = setInterval(function() { },100);
console.log(x);

See the circular references? They show up as [Circular]

In a browser environment, you'd get a number returned from setTimeout or setInterval, not the case when these functions are executed in node.

NodeJS timers documentation

Browser timers documentation (e.g. setTimeout)

Upvotes: 1

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