# SessionBuilder

Builds a transaction that deploys and executes WASM session code. Used for contract deployment and complex one-off operations.

## Import

```ts
import { SessionBuilder, Args, CLValue, PublicKey } from 'casper-js-sdk';
```

## Usage

```ts
import * as fs from 'fs';

const wasmBytes = fs.readFileSync('contract.wasm');

const args = Args.fromMap({
  token_name: CLValue.newCLString('MyToken'),
  token_symbol: CLValue.newCLString('MTK'),
  total_supply: CLValue.newCLUInt256('1000000000'),
});

const transaction = new SessionBuilder()
  .from(deployerPublicKey)
  .wasm(wasmBytes)
  .runtimeArgs(args)
  .chainName('casper')
  .payment(200_000_000_000)  // WASM deploys require more gas
  .build();

transaction.sign(privateKey);
const result = await rpcClient.putTransaction(transaction);
```

## Methods

### .from(publicKey)

- **Type:** `PublicKey` - required

### .wasm(bytes)

- **Type:** `Uint8Array` - required

The compiled WASM bytecode to execute.

### .runtimeArgs(args)

- **Type:** `Args` - optional

Arguments passed to the WASM's `call` function.

### .chainName(name)

- **Type:** `string` - required

### .payment(motes)

- **Type:** `number` - optional

WASM execution typically requires much higher gas than native transfers (50–500 CSPR depending on contract size and complexity).

## Return Value

`Transaction`

## Notes

- Session code runs in the context of the caller's account.
- Use `ContractCallBuilder` for calling already-deployed contracts.
- Gas costs scale with WASM size and execution complexity.

## Related

- [`ContractCallBuilder`](/builders/ContractCallBuilder)