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---
layout: api
id: promise.longstacktraces
title: Promise.longStackTraces
---


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## ~~Promise.longStackTraces~~

This method is deprecated. Use [Promise.config](/docs/api/promise.config.html) instead.

```js
Promise.config({
  longStackTraces: true
})
```

---

```js
Promise.longStackTraces() -> undefined
```

Call this right after the library is loaded to enable long stack traces. Long stack traces cannot be disabled after being enabled, and cannot be enabled after promises have already been created. Long stack traces imply a substantial performance penalty, around 4-5x for throughput and 0.5x for latency.

Long stack traces are enabled by default in the debug build.

To enable them in all instances of bluebird in node.js, use the environment variable `BLUEBIRD_DEBUG`:

```
BLUEBIRD_DEBUG=1 node server.js
```

Setting the environment variable `NODE_ENV` to `"development"` also automatically enables long stack traces.

You should enabled long stack traces if you want better debugging experience. For example:

```js
Promise.longStackTraces();
Promise.resolve().then(function outer() {
    return Promise.resolve().then(function inner() {
        return Promise.resolve().then(function evenMoreInner() {
            a.b.c.d()
        }).catch(function catcher(e) {
            console.error(e.stack);
        });
    });
});
```

Gives

    ReferenceError: a is not defined
        at evenMoreInner (<anonymous>:6:13)
    From previous event:
        at inner (<anonymous>:5:24)
    From previous event:
        at outer (<anonymous>:4:20)
    From previous event:
        at <anonymous>:3:9
        at Object.InjectedScript._evaluateOn (<anonymous>:581:39)
        at Object.InjectedScript._evaluateAndWrap (<anonymous>:540:52)
        at Object.InjectedScript.evaluate (<anonymous>:459:21)

While with long stack traces disabled, you would get:

    ReferenceError: a is not defined
        at evenMoreInner (<anonymous>:6:13)
        at tryCatch1 (<anonymous>:41:19)
        at Promise$_resolvePromise [as _resolvePromise] (<anonymous>:1739:13)
        at Promise$_resolveLast [as _resolveLast] (<anonymous>:1520:14)
        at Async$_consumeFunctionBuffer [as _consumeFunctionBuffer] (<anonymous>:560:33)
        at Async$consumeFunctionBuffer (<anonymous>:515:14)
        at MutationObserver.Promise$_Deferred (<anonymous>:433:17)

On client side, long stack traces currently only work in recent Firefoxes, Chrome and Internet Explorer 10+.
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