# Transaction manager

The `transactionManager` service is used to track a transaction's status as it propagates through the blockchain.

Methods in Dai.js that start transactions are asynchronous, so they return promises. These promises can be passed as arguments to the transaction manager to set up callbacks when transactions change their status to `pending`, `mined`, `confirmed` or `error`.

```javascript
const txMgr = maker.service('transactionManager');
// instance of transactionManager
const open = maker.service('cdp').openCdp();
// open is a promise--note the absence of `await`
```

Pass the promise to `transactionManager.listen` with callbacks, as shown below.

```javascript
txMgr.listen(open, {
  pending: tx => {
    // do something when tx is pending
  },
  mined: tx => {
    // do something when tx is mined
  },
  confirmed: tx => {
    // do something when tx is confirmed       
  },
  error: tx => {
    // do someting when tx fails
  }
});

await txMgr.confirm(open); 
// 'confirmed' callback will fire after 5 blocks
```

Note that the `confirmed` event will not fire unless `transactionManager.confirm` is called. This async function waits a number of blocks (default 5) after the transaction has been mined to resolve. To change this globally, set the `confirmedBlockCount` attribute in Maker [options](/build/dai.js/maker.md#options). To change it for just one call, pass the number of blocks to wait as the second argument:

```javascript
await txMgr.confirm(open, 3);
```

## Transaction Metadata

There are functions such as `lockEth()` which are composed of several internal transactions. These can be more accurately tracked by accessing `tx.metadata`in the callback which contains both the `contract` and the `method` the internal transactions were created from.

## Transaction Object Methods

A `TransactionObject` also has a few methods to provide further details on the transaction:

* `hash` : transaction hash
* `fees()` : amount of ether spent on gas
* `timeStamp()` : timestamp of when transaction was mined
* `timeStampSubmitted()` : timestamp of when transaction was submitted to the network

```javascript
const lock = cdp.lockEth(1);
txMgr.listen(lock, {
  pending: tx => {
    const {contract, method} = tx.metadata;
    if(contract === 'WETH' && method === 'deposit') {
      console.log(tx.hash); // print hash for WETH.deposit
    }
  }
})
```


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