# stack-trace

[![NPM Version](https://img.shields.io/npm/v/stack-trace.svg)](https://www.npmjs.com/package/stack-trace)
[![Tests](https://github.com/felixge/node-stack-trace/actions/workflows/test.yml/badge.svg)](https://github.com/felixge/node-stack-trace/actions/workflows/test.yml)

Get v8 stack traces as an array of CallSite objects.

## Install

``` bash
npm install stack-trace
```

## Usage

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

```javascript
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:

```javascript
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](https://github.com/tlrobinson/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](https://v8.dev/docs/stack-trace-api#customizing-stack-traces). 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.