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What is the error object?

by Mr. Nico Reed nicoreed on

The error object is a built-in object that provides a standard set of useful information when an error occurs, such as a stack trace and the error message. For example:

Code:

 var error = new Error("The error message");
 console.log(error);
 console.log(error.stack);

Result:

 { stack: [Getter/Setter],
   arguments: undefined,
   type: undefined,
   message: 'The error message' }
 Error: The error message
     at Object.<anonymous> (/home/nico/example.js:1:75)
     at Module._compile (module.js:407:26)
     at Object..js (module.js:413:10)
     at Module.load (module.js:339:31)
     at Function._load (module.js:298:12)
     at Array.0 (module.js:426:10)
     at EventEmitter._tickCallback (node.js:126:26)

error.stack shows you where an error came from, as well as a list of the function calls that preceded it - for your convenience, error.stack always prints error.message as the first line of its output, making error.stack a convenient single property to log during debugging.

If you want to add more information to the Error object, you can always add properities, just as with any other Javascript object:

var error = new Error("The error message");
error.http_code = 404;
console.log(error);

For more details how to use the Error object, check out the article on error conventions