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---
layout: api
id: error
title: .error
---


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<div class="api-code-section"><markdown>
##.error

```js
.error([function(any error) rejectedHandler]) -> Promise
```


Like [`.catch`](.) but instead of catching all types of exceptions, it only catches operational errors.

*Note, "errors" mean errors, as in objects that are `instanceof Error` - not strings, numbers and so on. See [a string is not an error](http://www.devthought.com/2011/12/22/a-string-is-not-an-error/).*

It is equivalent to the following [`.catch`](.) pattern:

```js
// Assumes OperationalError has been made global
function isOperationalError(e) {
    if (e == null) return false;
    return (e instanceof OperationalError) || (e.isOperational === true);
}

// Now this bit:
.catch(isOperationalError, function(e) {
    // ...
})

// Is equivalent to:

.error(function(e) {
    // ...
});
```

For example, if a promisified function errbacks the node-style callback with an error, that could be caught with [`.error`](.). However if the node-style callback **throws** an error, only `.catch` would catch that.

In the following example you might want to handle just the `SyntaxError` from JSON.parse and Filesystem errors from `fs` but let programmer errors bubble as unhandled rejections:

```js
var fs = Promise.promisifyAll(require("fs"));

fs.readFileAsync("myfile.json").then(JSON.parse).then(function (json) {
    console.log("Successful json")
}).catch(SyntaxError, function (e) {
    console.error("file contains invalid json");
}).error(function (e) {
    console.error("unable to read file, because: ", e.message);
});
```

Now, because there is no catch-all handler, if you typed `console.lag` (causes an error you don't expect), you will see:

```
Possibly unhandled TypeError: Object #<Console> has no method 'lag'
    at application.js:8:13
From previous event:
    at Object.<anonymous> (application.js:7:4)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:349:32)
    at Function.Module._load (module.js:305:12)
    at Function.Module.runMain (module.js:490:10)
    at startup (node.js:121:16)
    at node.js:761:3
```

*( If you don't get the above - you need to enable [long stack traces](/docs/api/promise.config.html) )*

And if the file contains invalid JSON:

```
file contains invalid json
```

And if the `fs` module causes an error like file not found:

```
unable to read file, because:  ENOENT, open 'not_there.txt'
```
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