error-callsites

error-callsites

Yet another module for extracting callsites (a.k.a. stack-frames) from Node.js Error objects.

Installation

npm install error-callsites

Usage

var callsites = require('error-callsites')

var err = new Error('foo')
var frames = callsites(err)

console.log('Error occurred on line', frames[0].getLineNumber())

API

The module exposes a single function which expects an Error object as the first argument:

var frames = callsites(err)

More specifically, it expects an object on which Error.captureStackTrace(obj) has been called, which is the case for Error objects. You can do it directly yourself:

var obj = {}
Error.captureStackTrace(obj)
var frames = callsites(err)

The function returns an array of v8 CallSite objects -- one for each frame in the stack trace. CallSite objects provide accessor methods for information on that frame. For example:

• callsite.getThis() - returns the value of this
• callsite.getTypeName() - returns the type of this as a string. This is the name of the function stored in the constructor field of this, if available, otherwise the object's [[Class]] internal property.
• callsite.getFunction() - returns the current function
• callsite.getFunctionName() - returns the name of the current function, typically its name property. If a name property is not available an attempt will be made to try to infer a name from the function's context.
• callsite.getMethodName() - returns the name of the property of this or one of its prototypes that holds the current function
• callsite.getFileName() - if this function was defined in a script returns the name of the script
• callsite.getLineNumber() - if this function was defined in a script returns the current line number
• callsite.getColumnNumber() - if this function was defined in a script returns the current column number
• callsite.getEvalOrigin() - if this function was created using a call to eval returns a CallSite object representing the location where eval was called
• callsite.isToplevel() - is this a toplevel invocation, that is, is this the global object?
• callsite.isEval() - does this call take place in code defined by a call to eval?
• callsite.isNative() - is this call in native V8 code?
• callsite.isConstructor() - is this a constructor call?

See the link above for a complete list of the accessor methods. Some have been added in more recent versions of v8 and Node.js.

How it works

This package works by setting a custom Error.prepareStackTrace property that transparently captures the structured stack trace that v8 passes to this API, while also supporting other Node.js code in the process setting its own Error.prepareStackTrace.

License

MIT