I wrote the solidity function below to swap ether for other tokens on a Uniswap exchange. It works.

function buyCryptoOnUniswap1(uint256 etherCost , address cryptoToken) public payable returns (uint256) {

  IUniswapV2Router02 usi = IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
   if(etherCost > address(this).balance){
          return 0;
    uint deadline = now + 300; // using 'now' for convenience, for mainnet pass deadline from frontend!
    uint[] memory amounts = usi.swapExactETHForTokens.value(etherCost)(0, getPathForETHToToken(cryptoToken), address(this), deadline);
    uint256 outputTokenCount = uint256(amounts[1]);
    return outputTokenCount;

  function getPathForETHToToken(address crypto) private view returns (address[] memory) {
    address[] memory path = new address[](2);
    path[0] = usi.WETH();
    path[1] = crypto;
    return path;

According to the docs, the returned value called amounts is an array of uints which consists of the input token amount and all subsequent output token amounts.

amounts, uint[] memory, The input token amount and all subsequent output token amounts.

So I hazarded a guess as to it(the number of purchased tokens) been in index 1 of the return value.

Please how do I get the number of tokens returned by this transaction?

Sorry, but it doesn't seem so clear from the documentation..


1 Answer 1


It is obviously the amount of the last token in the path, i.e., amounts[amounts.length - 1].

  • Thanks. I wanted to be sure, so that I would not be surprised in production. Thanks again Commented Jul 4, 2020 at 13:02

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