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Using the BEX SDK, you can add liquidity using two primary methods (see AddLiquidityKind):
  1. Unbalanced - add liquidity with arbitrary amounts of each token
  2. Proportional - add liquidity with proportional amount of both tokens
For more comprehensive add liquidity examples, see the add liquidity examples in the BEX SDK repository. For price impact calculation examples, see the price impact examples.

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Example: adding unbalanced liquidity

In this example, we use the BEX SDK and Ethers.js to add single-token BERA liquidity to a given pool. 
import { ethers } from "ethers";
import {
  BalancerApi,
  AddLiquidity,
  AddLiquidityKind,
  Slippage,
  PriceImpact,
} from "@berachain-foundation/berancer-sdk";

// Initialize provider and wallet
const RPC_URL = "https://rpc.berachain.com/";
const provider = new ethers.JsonRpcProvider(RPC_URL);
const wallet = new ethers.Wallet(process.env.PRIVATE_KEY, provider);
const balancerApi = new BalancerApi("https://chgbtcc9ffu7rbdw2kmu4urwy.stellate.sh/", 80094);

// Get pool data
const poolId =
  "POOL_ID";
const poolState = await balancerApi.pools.fetchPoolState(poolId);

// Prepare add liquidity input - note we're only adding one token for unbalanced
const addLiquidityInput = {
  chainId: CHAIN_ID,
  kind: AddLiquidityKind.Unbalanced,
  rpcUrl: RPC_URL,
  amountsIn: [
    {
      address: WBERA_TOKEN,
      decimals: 18,
      rawAmount: ethers.parseUnits("0.1", 18), // 0.1 BERA
    },
  ],
};

const addLiquidity = new AddLiquidity();

// Query expected BPT out and calculate price impact in parallel
const [queryOutput, priceImpact] = await Promise.all([
  addLiquidity.query(addLiquidityInput, poolState),
  PriceImpact.addLiquidity(addLiquidityInput, poolState)
]);

console.log(
  "Expected BPT Out:",
  ethers.formatUnits(queryOutput.bptOut.amount, 18)
);
console.log("Price Impact:", priceImpact.percentage, "%");

// Build transaction with 1% slippage
const slippage = Slippage.fromPercentage("1");
const deadline = BigInt(Math.floor(Date.now() / 1000) + 60);

const callData = addLiquidity.buildCall({
  ...queryOutput,
  chainId: CHAIN_ID,
  sender: wallet.address,
  poolId: poolState.id,
  recipient: wallet.address,
  wethIsEth: true,
  slippage,
  deadline,
});

// Send transaction
const tx = await wallet.sendTransaction({
  to: callData.to,
  data: callData.callData,
  value: callData.value,
});

console.log("Transaction sent:", tx.hash);

const receipt = await tx.wait();
Below we breakdown the code example above.

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Helper classes

The main helper classes we use from the SDK are:
  • BalancerApi - to simplify retrieving pool data from the Pools API
  • AddLiquidity - to build addLiquidity queries and transactions
  • Slippage - to simplify creating limits with user defined slippage
  • PriceImpact - to calculate the price impact of unbalanced liquidity additions

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Fetching pool data

After initializing the BalancerApi class, we can fetch current pool data using fetchPoolState. 
const balancerApi = new BalancerApi("https://chgbtcc9ffu7rbdw2kmu4urwy.stellate.sh/", 80094);

// Get pool data
const poolId =
  "POOL_ID";
const poolState = await balancerApi.pools.fetchPoolState(poolId);

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Simulation and price impact

The AddLiquidity class has a query method that allows us to simulate the add liquidity transaction. This is useful for estimating the expected output and slippage. It takes in the addLiquidityInput and poolState as arguments. The PriceImpact class calculates the price impact of unbalanced liquidity operations. When adding liquidity with unbalanced amounts (adding only one token or different proportions than the pool), the pool’s token ratios change, resulting in price impact. A PriceImpactAmount is returned, with the price impact expressed in a number of different units. 
// Query expected BPT out and calculate price impact in parallel
const [queryOutput, priceImpact] = await Promise.all([
  addLiquidity.query(addLiquidityInput, poolState),
  PriceImpact.addLiquidity(addLiquidityInput, poolState)
]);

console.log("Expected BPT Out:", ethers.formatUnits(queryOutput.bptOut.amount, 18));
console.log("Price Impact:", priceImpact.percentage, "%");

// Build transaction with 1% slippage
const slippage = Slippage.fromPercentage("1");
The price impact calculation is especially important for unbalanced liquidity additions, as they can significantly alter the pool’s token ratios. Use this information to inform your slippage settings and warn about potential price impacts.

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Building the transaction

The AddLiquidity class has a buildCall method that allows us to build the transaction. This method takes in the queryOutput and address parameters. 
const callData = addLiquidity.buildCall({
  ...queryOutput,
  sender: wallet.address,
  recipient: wallet.address,
  wethIsEth: true,
  slippage,
  deadline
});

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Adding proportional liquidity

Adding proportional liquidity is similar to adding unbalanced liquidity, but instead of specifying the amount of each token, you specify a referenceAmount for one of the tokens. (see AddLiquidityProportionalInput) The SDK will then calculate the amount of the other token to add based on the current pool composition. 
addLiquidityInput = {
    chainId,
    kind: AddLiquidityKind.Proportional,
    rpcUrl: RPC_URL,
    referenceAmount: {
        rawAmount: parseUnits(tokenAmount, tokenDecimals),
        decimals: tokenDecimals,
        address: tokenAddress,
    },
};