felixge/node-stack-trace

stack-trace

Get v8 stack traces as an array of CallSite objects.

Install

npm install stack-trace

Usage

The stack-trace module makes it easy for you to capture the current stack:

import { get } from 'stack-trace';
const trace = get();

expect(trace[0].getFileName()).toBe(__filename);

However, sometimes you have already popped the stack you are interested in, and all you have left is an Error object. This module can help:

import { parse } from 'stack-trace';
const err = new Error('something went wrong');
const trace = parse(err);

expect(trace[0].getFileName()).toBe(__filename);

Please note that parsing the Error#stack property is not perfect, only certain properties can be retrieved with it as noted in the API docs below.

Long stack traces

When parsing an err.stack that has crossed the event loop boundary, a CallSite object is created whose getFileName() returns the full dashed separator line from the stack, including any leading whitespace such as indentation. The other getter-style methods of the event loop boundary call site return null.

Historically this behavior was often observed together with long-stack-traces, but that package is unmaintained. This module does not depend on it and still supports parsing dashed event-loop boundary markers when they are present in the stack string.

API

stackTrace.get([belowFn])

Returns an array of CallSite objects, where element 0 is the current call site.

When passing a function on the current stack as the belowFn parameter, the returned array will only include CallSite objects below this function.

stackTrace.parse(err)

Parses the err.stack property of an Error object into an array compatible with those returned by stackTrace.get(). However, only the following methods are implemented on the returned CallSite objects.

• getTypeName
• getFunctionName
• getMethodName
• getFileName
• getLineNumber
• getColumnNumber
• isNative

Note: Except getFunctionName(), all of the above methods return exactly the same values as you would get from stackTrace.get(). getFunctionName() is sometimes a little different, but still useful.

CallSite

The official v8 CallSite object API can be found in the V8 stack trace API docs. A quick excerpt:

A CallSite object defines the following methods:

• getThis: returns the value of this
• 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.
• getFunction: returns the current function
• 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.
• getMethodName: returns the name of the property of this or one of its prototypes that holds the current function
• getFileName: if this function was defined in a script returns the name of the script
• getLineNumber: if this function was defined in a script returns the current line number
• getColumnNumber: if this function was defined in a script returns the current column number
• getEvalOrigin: if this function was created using a call to eval returns a CallSite object representing the location where eval was called
• isToplevel: is this a toplevel invocation, that is, is this the global object?
• isEval: does this call take place in code defined by a call to eval?
• isNative: is this call in native V8 code?
• isConstructor: is this a constructor call?

License

stack-trace is licensed under the MIT license.