Syntax

exchange.IO("logs", ...)

Queries the event logs of a contract (eth_getLogs) and decodes them according to the ABI. It supports filtering by block range and by the indexed parameters of events, and can be used to monitor on-chain events such as trades, incoming transfers, and liquidity pool changes.


    
    
    
exchange.IO(k, query)

Examples

Query USDC transfer events and Swap events of a Uniswap liquidity pool.


    javascript
    
    
function main() {
    var USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
    var POOL = "0x88e6A0c2dDD26FEEb64F039a2c41296FcB3f5640"   // Uniswap V3 USDC/WETH 0.05% pool

    // The Transfer event of tokens is supported natively; a negative fromBlock indicates an offset
    // relative to the latest block
    var transfers = exchange.IO("logs", { address: USDC, event: "Transfer", fromBlock: -2 })
    Log("USDC transfers in the last 3 blocks:", transfers.length, "entries")
    if (transfers.length > 0) {
        var t = transfers[0]
        Log(t.blockNumber, t.transactionHash, t.args.from, "→", t.args.to, t.args.value)
        // Filter by indexed parameters
        var mine = exchange.IO("logs", { address: USDC, event: "Transfer", fromBlock: -2,
            filter: { from: t.args.from } })
        Log("Same sender:", mine.length, "entries")
    }

    // For events of other contracts, the ABI containing the event must be registered first
    exchange.IO("abi", POOL, JSON.stringify([{ type: "event", name: "Swap", anonymous: false,
        inputs: [
        { indexed: true, name: "sender", type: "address" }, { indexed: true, name: "recipient",
            type: "address" },
        { indexed: false, name: "amount0", type: "int256" }, { indexed: false, name: "amount1",
            type: "int256" },
        { indexed: false, name: "sqrtPriceX96", type: "uint160" }, { indexed: false,
            name: "liquidity", type: "uint128" },
        { indexed: false, name: "tick", type: "int24" }] }]))
    var swaps = exchange.IO("logs", { address: POOL, event: "Swap", fromBlock: -20 })
    swaps.forEach(function (s) {
        Log("Swap block", s.blockNumber, "amount0:", s.args.amount0, "amount1:", s.args.amount1,
            "tick:", s.args.tick)
    })
}

Returns

Type	Description
array	Returns an array of logs. Each entry contains `address` (lowercase), `blockNumber`, `logIndex`, `transactionIndex` (numbers), `transactionHash`, `blockHash`, `topics`, `data` and `removed`, plus `event` (the event name) and `args` (the arguments) when it can be decoded by an ABI.

Arguments

Name	Type	Required	Description
k	string	Yes	Function of the `exchange.IO()` function. When set to `logs`, it indicates that the function is used to query event logs.
query	object	Yes	Query conditions: `address` is the contract address (a string or an array); `event` is the event name or the full event signature (for example, `"Transfer(address,address,uint256)"`); `filter` is an object for filtering by indexed parameter names, and when a value is an array, it matches any one of the values in it; `fromBlock` and `toBlock` are used to specify the block range (they can be numbers or tags such as `latest`; a negative number indicates an offset relative to the latest block, and both default to `latest`); `topics` or `blockHash` can also be set directly.