智能合约dapp开发技术主要由以太坊区块链网络提供支持，该网络提供了一系列的智能合约技术，这些智能合约可以让开发者快速、安全地构建出功能强大的dapp。
智能合约dapp开发技术主要包括以太坊智能合约语言Solidity，以太坊智能合约框架Truffle，Web3.js，以太坊区块链浏览器Mist等
智能合约：它们是存储在区块链上的计算机程序，在满足预定条件时运行，智能合约是用Solidity语言编写的。
web3.js是一个JavaScript API库。要让DApp在以太坊上运行，我们可以使用web3.js库提供的web3对象。web3.js通过RPC调用与本地节点通信，它可以与任何公开RPC层的以太坊节点一起使用。web3包含eth对象-web3.eth（用于与以太坊区块链交互）和shh对象-web3.shh（用于与Whisper交互）
//this low-level function should be called from a contract which performs important safety checks
function burn(address to)external lock returns(uint amount0,uint amount1){
(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings
address _token0=token0;//gas savings
address _token1=token1;//gas savings
uint balance0=IERC20(_token0).balanceOf(address(this));
uint balance1=IERC20(_token1).balanceOf(address(this));
uint liquidity=balanceOf[address(this)];
bool feeOn=_mintFee(_reserve0,_reserve1);
uint _totalSupply=totalSupply;//gas savings,must be defined here since totalSupply can update in _mintFee
amount0=liquidity.mul(balance0)/_totalSupply;//using balances ensures pro-rata distribution
amount1=liquidity.mul(balance1)/_totalSupply;//using balances ensures pro-rata distribution
require(amount0>0&&amount1>0,'UniswapV2:INSUFFICIENT_LIQUIDITY_BURNED');
_burn(address(this),liquidity);
_safeTransfer(_token0,to,amount0);
_safeTransfer(_token1,to,amount1);
balance0=IERC20(_token0).balanceOf(address(this));
balance1=IERC20(_token1).balanceOf(address(this));
_update(balance0,balance1,_reserve0,_reserve1);
if(feeOn)kLast=uint(reserve0).mul(reserve1);//reserve0 and reserve1 are up-to-date
emit Burn(msg.sender,amount0,amount1,to);
}
//this low-level function should be called from a contract which performs important safety checks
function swap(uint amount0Out,uint amount1Out,address to,bytes calldata data)external lock{
require(amount0Out>0||amount1Out>0,'UniswapV2:INSUFFICIENT_OUTPUT_AMOUNT');
(uint112 _reserve0,uint112 _reserve1,)=getReserves();//gas savings
require(amount0Out<_reserve0&&amount1Out<_reserve1,'UniswapV2:INSUFFICIENT_LIQUIDITY');
uint balance0;
uint balance1;
{//scope for _token{0,1},avoids stack too deep errors
address _token0=token0;
address _token1=token1;
require(to!=_token0&&to!=_token1,'UniswapV2:INVALID_TO');
if(amount0Out>0)_safeTransfer(_token0,to,amount0Out);//optimistically transfer tokens
if(amount1Out>0)_safeTransfer(_token1,to,amount1Out);//optimistically transfer tokens
if(data.length>0)IUniswapV2Callee(to).uniswapV2Call(msg.sender,amount0Out,amount1Out,data);
balance0=IERC20(_token0).balanceOf(address(this));
balance1=IERC20(_token1).balanceOf(address(this));
}
uint amount0In=balance0>_reserve0-amount0Out?balance0-(_reserve0-amount0Out):0;
uint amount1In=balance1>_reserve1-amount1Out?balance1-(_reserve1-amount1Out):0;
require(amount0In>0||amount1In>0,'UniswapV2:INSUFFICIENT_INPUT_AMOUNT');
{//scope for reserve{0,1}Adjusted,avoids stack too deep errors
uint balance0Adjusted=balance0.mul(1000).sub(amount0In.mul(3));
uint balance1Adjusted=balance1.mul(1000).sub(amount1In.mul(3));
require(balance0Adjusted.mul(balance1Adjusted)>=uint(_reserve0).mul(_reserve1).mul(1000**2),'UniswapV2:K');
}
_update(balance0,balance1,_reserve0,_reserve1);
emit Swap(msg.sender,amount0In,amount1In,amount0Out,amount1Out,to);
}
//force balances to match reserves
function skim(address to)external lock{
address _token0=token0;//gas savings
address _token1=token1;//gas savings
_safeTransfer(_token0,to,IERC20(_token0).balanceOf(address(this)).sub(reserve0));
_safeTransfer(_token1,to,IERC20(_token1).balanceOf(address(this)).sub(reserve1));
}
//force reserves to match balances
function sync()external lock{
_update(IERC20(token0).balanceOf(address(this)),IERC20(token1).balanceOf(address(this)),reserve0,reserve1);
}
}
