Error comparison and information related utility for node and the browser.
## What is Check-Error?
Check-Error is a module which you can use to retrieve an Error's information such as its `message` or `constructor` name and also to check whether two Errors are compatible based on their messages, constructors or even instances.
## Installation
### Node.js
`check-error` is available on [npm](http://npmjs.org). To install it, type:
$ npm install check-error
### Browsers
You can also use it within the browser; install via npm and use the `check-error.js` file found within the download. For example:
```html
```
## Usage
The primary export of `check-error` is an object which has the following methods:
* `compatibleInstance(err, errorLike)` - Checks if an error is compatible with another `errorLike` object. If `errorLike` is an error instance we do a strict comparison, otherwise we return `false` by default, because instances of objects can only be compatible if they're both error instances.
* `compatibleConstructor(err, errorLike)` - Checks if an error's constructor is compatible with another `errorLike` object. If `err` has the same constructor as `errorLike` or if `err` is an instance of `errorLike`.
* `compatibleMessage(err, errMatcher)` - Checks if an error message is compatible with an `errMatcher` RegExp or String (we check if the message contains the String).
* `getConstructorName(errorLike)` - Retrieves the name of a constructor, an error's constructor or `errorLike` itself if it's not an error instance or constructor.
* `getMessage(err)` - Retrieves the message of an error or `err` itself if it's a String. If `err` or `err.message` is undefined we return an empty String.
```js
var checkError = require('check-error');
```
#### .compatibleInstance(err, errorLike)
```js
var checkError = require('check-error');
var funcThatThrows = function() { throw new TypeError('I am a TypeError') };
var caughtErr;
try {
funcThatThrows();
} catch(e) {
caughtErr = e;
}
var sameInstance = caughtErr;
checkError.compatibleInstance(caughtErr, sameInstance); // true
checkError.compatibleInstance(caughtErr, new TypeError('Another error')); // false
```
#### .compatibleConstructor(err, errorLike)
```js
var checkError = require('check-error');
var funcThatThrows = function() { throw new TypeError('I am a TypeError') };
var caughtErr;
try {
funcThatThrows();
} catch(e) {
caughtErr = e;
}
checkError.compatibleConstructor(caughtErr, Error); // true
checkError.compatibleConstructor(caughtErr, TypeError); // true
checkError.compatibleConstructor(caughtErr, RangeError); // false
```
#### .compatibleMessage(err, errMatcher)
```js
var checkError = require('check-error');
var funcThatThrows = function() { throw new TypeError('I am a TypeError') };
var caughtErr;
try {
funcThatThrows();
} catch(e) {
caughtErr = e;
}
var sameInstance = caughtErr;
checkError.compatibleMessage(caughtErr, /TypeError$/); // true
checkError.compatibleMessage(caughtErr, 'I am a'); // true
checkError.compatibleMessage(caughtErr, /unicorn/); // false
checkError.compatibleMessage(caughtErr, 'I do not exist'); // false
```
#### .getConstructorName(errorLike)
```js
var checkError = require('check-error');
var funcThatThrows = function() { throw new TypeError('I am a TypeError') };
var caughtErr;
try {
funcThatThrows();
} catch(e) {
caughtErr = e;
}
var sameInstance = caughtErr;
checkError.getConstructorName(caughtErr) // 'TypeError'
```
#### .getMessage(err)
```js
var checkError = require('check-error');
var funcThatThrows = function() { throw new TypeError('I am a TypeError') };
var caughtErr;
try {
funcThatThrows();
} catch(e) {
caughtErr = e;
}
var sameInstance = caughtErr;
checkError.getMessage(caughtErr) // 'I am a TypeError'
```
check-error