# Flash Loans SDK

*[Documentation index](/llms.txt) · [Full index](/llms-full.txt)*

A flash loan is one where the borrowing and returning of loans from pools is performed within a single programmable transaction block. The SDK exposes functions that allow you to implement this functionality. See [Flash Loans](/onchain-finance/deepbookv3/contract-information/flash-loans) for more details on the API.

## Flash loan functions

The DeepBookV3 SDK provides the following flash loan related functions.

### borrowBaseAsset

Use `borrowBaseAsset` to borrow a base asset from the pool identified by the `poolKey` value you provide. The call returns a function that takes a `Transaction` object

**Parameters**

- `poolKey`: String that identifies the pool from which to borrow.
- `borrowAmount`: Number that represents the amount to borrow from the pool.

```tsx
borrowBaseAsset(poolKey: string, borrowAmount: number);
```

### returnBaseAsset

Use `returnBaseAsset` to return the base asset to the pool identified by the `poolKey` value you provide. The call returns a function that takes a `Transaction` object.

**Parameters**

- `poolKey`: String that identifies the pool from which to borrow.
- `borrowAmount`: Number that represents the amount to borrow from the pool.
- `baseCoinInput`: Coin object representing the base asset to be returned.
- `flashLoan`: Flash loan object representing the loan to be settled.

```tsx
returnBaseAsset(
  {
    poolKey: string,
    borrowAmount: number,
    baseCoinInput: TransactionObjectArgument,
    flashLoan: TransactionObjectArgument,
  }
)
```

### borrowQuoteAsset

Use `borrowQuoteAsset` to borrow a quote asset from the pool identified by the `poolKey` value you provide. The call returns a function that takes a `Transaction` object.

**Parameters**

- `poolKey`: String that identifies the pool from which to borrow.
- `borrowAmount`: Number that represents the amount to borrow from the pool.

```tsx
borrowQuoteAsset(poolKey: string, borrowAmount: number);
```

### returnQuoteAsset

Use `returnQuoteAsset` to return a quote asset to the pool identified by the `poolKey` you provide. The call returns a function that takes a `Transaction` object.

**Parameters**

- `poolKey`: String that identifies the pool from which to borrow.
- `borrowAmount`: Number that represents the amount to borrow from the pool.
- `baseCoinInput`: Coin object representing the quote asset to be returned.
- `flashLoan`: Flash loan object representing the loan to be settled.

```tsx
returnQuoteAsset(
  poolKey: string,
  borrowAmount: number,
  quoteCoinInput: TransactionObjectArgument,
  flashLoan: TransactionObjectArgument,
);
```

## Flash loan example

The following example demonstrates flash loan usage in `DeepBookMarketMaker` class.

```tsx
// Example of a flash loan transaction
// Borrow 1 DEEP from DEEP_SUI pool
// Swap 0.5 DBUSDC for SUI in SUI_DBUSDC pool, pay with deep borrowed
// Swap SUI back to DEEP
// Return 1 DEEP to DEEP_SUI pool
flashLoanExample = async (tx: Transaction) => {
  const borrowAmount = 1;
  const [deepCoin, flashLoan] = tx.add(this.flashLoans.borrowBaseAsset('DEEP_SUI', borrowAmount));

  // Execute trade using borrowed DEEP
  const [baseOut, quoteOut, deepOut] = tx.add(
    this.deepBook.swapExactQuoteForBase({
      poolKey: 'SUI_DBUSDC',
      amount: 0.5,
      deepAmount: 1,
      minOut: 0,
      deepCoin: deepCoin,
    }),
  );

  tx.transferObjects([baseOut, quoteOut, deepOut], this.getActiveAddress());

  // Execute second trade to get back DEEP for repayment
  const [baseOut2, quoteOut2, deepOut2] = tx.add(
    this.deepBook.swapExactQuoteForBase({
      poolKey: 'DEEP_SUI',
      amount: 10,
      deepAmount: 0,
      minOut: 0,
    }),
  );

  tx.transferObjects([quoteOut2, deepOut2], this.getActiveAddress());

  // Return borrowed DEEP
  const loanRemain = tx.add(
    this.flashLoans.returnBaseAsset('DEEP_SUI', borrowAmount, baseOut2, flashLoan),
  );

  // Send the remaining coin to user's address
  tx.transferObjects([loanRemain], this.getActiveAddress());
};
```