espower

espower
================================

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Power Assert feature instrumentor based on the ECMAScript AST.

DESCRIPTION
---------------------------------------
espower is a core module of power-assert family.

espower detects and manipulates assertion expression (JavaScript Code) in the form of ECMAScript AST defined in The ESTree Spec (formerly known as Mozilla SpiderMonkey Parser API), to instrument power-assert feature into returned new AST object. AST in, AST out. Since 0.11.0, espower can transform ES6 AST as well.

Pull-requests, issue reports and patches are always welcomed. See power-assert project for more documentation.

CHANGELOG
---------------------------------------
See CHANGELOG

API
---------------------------------------

$3

| return type |
|:------------|
| object |

espower function manipulates ast then returns modifiedAst that is also an AST node object defined in The ESTree Spec. ast will be manipulated directly and returned modifiedAst will be the same instance of ast.

espower function throws EspowerError when

* ast is already instrumented
* ast does not contain location information
* options argument is not valid

$3

| return type |
|:------------|
| object |

espower.createVisitor generates visitor object to be used with estraverse.replace. Arguments are the same as espower function.

#### ast

| type | default value |
|:---------|:--------------|
| object | N/A |

ast should be an AST node object defined in The ESTree Spec.

#### options

| type | default value |
|:---------|:--------------|
| object | (return value of espower.defaultOptions()) |

Configuration options. If not passed, default options will be used.

#### options.patterns

| type | default value |
|:--------------------|:--------------------|
| Array of string | objects shown below |

``javascript
[
'assert(value, [message])',
'assert.ok(value, [message])',
'assert.equal(actual, expected, [message])',
'assert.notEqual(actual, expected, [message])',
'assert.strictEqual(actual, expected, [message])',
'assert.notStrictEqual(actual, expected, [message])',
'assert.deepEqual(actual, expected, [message])',
'assert.notDeepEqual(actual, expected, [message])',
'assert.deepStrictEqual(actual, expected, [message])',
'assert.notDeepStrictEqual(actual, expected, [message])'
]
`

Target patterns for power assert feature instrumentation.

If callee name (for example, assert.equal) matches exactly and number of arguments is satisfied, then the assertion will be modified.
Detection is done by escallmatch. Any arguments enclosed in bracket (for example, [message]) means optional parameters. Without bracket means mandatory parameters.


#### options.ecmaVersion

| type | default value |
|:---------|:--------------|
| number | 2018 |

The ECMAScript version to parse and analyze. Must be either 3, 5, 6 (2015), 2016, 2017, or 2018.


#### options.sourceType

| type | default value |
|:---------|:--------------|
| string | 'module' |

The source type of the code. Must be either "script" or "module".


#### (optional) options.path

| type | default value |
|:---------|:--------------|
| string | N/A |

Filepath of originalAst. If passed, espower stores filepath information for reporting. If options.path is absolute and it conflicts with options.sourceRoot or sourceRoot in options.sourceMap, then filepath in power-assert output will be fall back on basename of options.path. This property is optional.


#### (optional) options.sourceRoot

| type | default value |
|:---------|:--------------|
| string | N/A |

Root filepath for target test files. Only works with options.path or options.sourceMap. If set, filepath in power-assert output will be relative from options.sourceRoot. When both options.sourceRoot and sourceMap's sourceRoot are given and both are absolute filepath, options.sourceRoot has precedence over sourceMap's sourceRoot. This property is optional.


#### (optional) options.sourceMap

| type | default value |
|:--------------------|:--------------|
| object or string| N/A |

A raw (either as a string which can be JSON.parse'd, or an object) SourceMap associated with originalAst. This property is optional. If given, espower uses options.sourceMap to adjust information in the power-assert output.


#### (optional) options.visitorKeys

| type | default value |
|:---------|:--------------|
| object | N/A |

VisitorKeys for AST traversal. See estraverse.VisitorKeys and babel.types.VISITOR_KEYS.

$3

Returns default options object for espower function. In other words, returns

`javascript
{
ecmaVersion: 2018,
sourceType: 'module',
patterns: [
'assert(value, [message])',
'assert.ok(value, [message])',
'assert.equal(actual, expected, [message])',
'assert.notEqual(actual, expected, [message])',
'assert.strictEqual(actual, expected, [message])',
'assert.notStrictEqual(actual, expected, [message])',
'assert.deepEqual(actual, expected, [message])',
'assert.notDeepEqual(actual, expected, [message])',
'assert.deepStrictEqual(actual, expected, [message])',
'assert.notDeepStrictEqual(actual, expected, [message])'
]
}
`


EXAMPLE
---------------------------------------

For given test file example_test.js below,

`javascript
var assert = require('power-assert');
var truthy = 'true';
var falsy = 'false';
assert(falsy);
assert.equal(truthy, falsy);
`

Apply espower then generate modified code to console,

`javascript
var espower = require('espower');
var esprima = require('esprima');
var escodegen = require('escodegen');
var fs = require('fs');
var path = require('path');

var filepath = path.join(__dirname, 'example_test.js');
var jsAst = esprima.parse(fs.readFileSync(filepath), {tolerant: true, loc: true, tokens: true});
var modifiedAst = espower(jsAst, {path: filepath, sourceRoot: __dirname});

console.log(escodegen.generate(modifiedAst));
`

Output:

`javascript
var _PowerAssertRecorder1 = function () {
function PowerAssertRecorder() {
this.captured = [];
}
PowerAssertRecorder.prototype._capt = function _capt(value, espath) {
this.captured.push({
value: value,
espath: espath
});
return value;
};
PowerAssertRecorder.prototype._expr = function _expr(value, source) {
var capturedValues = this.captured;
this.captured = [];
return {
powerAssertContext: {
value: value,
events: capturedValues
},
source: source
};
};
return PowerAssertRecorder;
}();
var _rec1 = new _PowerAssertRecorder1();
var _rec2 = new _PowerAssertRecorder1();
var _rec3 = new _PowerAssertRecorder1();
var assert = require('power-assert');
var truthy = 'true';
var falsy = 'false';
assert(_rec1._expr(_rec1._capt(falsy, 'arguments/0'), {
content: 'assert(falsy)',
filepath: 'example_test.js',
line: 4
}));
assert.equal(_rec2._expr(_rec2._capt(truthy, 'arguments/0'), {
content: 'assert.equal(truthy, falsy)',
filepath: 'example_test.js',
line: 5
}), _rec3._expr(_rec3._capt(falsy, 'arguments/1'), {
content: 'assert.equal(truthy, falsy)',
filepath: 'example_test.js',
line: 5
}));
``

INSTALL
---------------------------------------

$3

Install

$ npm install --save-dev espower

OUR SUPPORT POLICY
---------------------------------------

We support Node under maintenance. In other words, we stop supporting old Node version when their maintenance ends.

This means that any other environment is not supported.

NOTE: If espower works in any of the unsupported environments, it is purely coincidental and has no bearing on future compatibility. Use at your own risk.

AUTHOR
---------------------------------------
* Takuto Wada

CONTRIBUTORS
---------------------------------------
* James Talmage (jamestalmage)

LICENSE
---------------------------------------
Licensed under the MIT license.

[npm-url]: https://npmjs.org/package/espower
[npm-image]: https://badge.fury.io/js/espower.svg

[travis-url]: https://travis-ci.org/power-assert-js/espower
[travis-image]: https://secure.travis-ci.org/power-assert-js/espower.svg?branch=master

[depstat-url]: https://gemnasium.com/power-assert-js/espower
[depstat-image]: https://gemnasium.com/power-assert-js/espower.svg

[license-url]: https://github.com/power-assert-js/espower/blob/master/MIT-LICENSE.txt
[license-image]: https://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat

[codeclimate-url]: https://codeclimate.com/github/power-assert-js/espower
[codeclimate-image]: https://codeclimate.com/github/power-assert-js/espower/badges/gpa.svg

[coverage-url]: https://coveralls.io/r/power-assert-js/espower?branch=master
[coverage-image]: https://coveralls.io/repos/power-assert-js/espower/badge.svg?branch=master