swap.js

function swapETHToDai() public payable returns(uint[] memory) {
    // static array: address[k] memory array;
    // The following is the dynamic array way of initialization
    address[] memory _paths = new address[](2);
    // Also, push() is for storage array.
    _paths[0] = WETHAddress;
    _paths[1] = DaiAddress;
    return uniswapV2Router01.swapExactETHForTokens{value: msg.value}(0, _paths, msg.sender, now + 120);
}

function swapDaiForETH(uint _DaiAmount) public returns(uint[] memory) {
    require(Dai.transferFrom(msg.sender, address(this), _DaiAmount));
    address[] memory _paths = new address[](2);
    _paths[0] = DaiAddress;
    _paths[1] = WETHAddress;
    Dai.approve(address(uniswapV2Router01), _DaiAmount);
    return uniswapV2Router01.swapExactTokensForETH(_DaiAmount, 0, _paths, msg.sender, now + 120);
}

Hello Aleks, I use the ERC20 interface from openzeppelin: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol *require(Dai.transferFrom(msg.sender, address(this), _DaiAmount));Is this idea that I first send tokens from my metamask wallet to my contract? * -> Yep. As a reminder, before transferFrom(), you have to use the approve() function of the desired ERC20 (Dai in this example), so that you will not get an error while using transferFrom(). *Dai.approve(address(uniswapV2Router01), _DaiAmount);Is here the idea that I approve that the uniswap router spends these tokens after I have approved it? * -> You're right! Best regards, Shao alberentsen <notifications@github.com> 於 2020年6月6日 週六 上午1:35寫道：

…

***@***.**** commented on this gist. ------------------------------ Hi Tien I was looking for an example that uses swap.ExactTokensForETH so I found you. I had no problem to replicate the function swapETHToDai() but the function swapDaiForETH is not working. One reason is that you use the ERC20 interface while I use the IERC20 interface from zeppelin. What ERC20 interface do you use? I have also difficulty to figure out the meaning of: require(Dai.transferFrom(msg.sender, address(this), _DaiAmount)); Is this idea that I first send tokens from my metamask wallet to my contract? Dai.approve(address(uniswapV2Router01), _DaiAmount); Is here the idea that I approve that the uniswap router spends these tokens after I have approved it? As you can see I'm a beginner in solidity and I have very little programming background. Anyhow, it would be very helpful if you could help me in this matter. Best wishes aleks — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3331237>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR3RCQCYABI3ZC5K7LTRVEUFJANCNFSM4NUNZ4FQ> .

Dear Aleks, I'm glad that I can help you! If you have any more questions about Uniswap, Compound, and other DeFi projects, I am willing to discuss them with you. Best regards, Tien Shao Ku Master's student in Computer Science National Cheng Kung University alberentsen <notifications@github.com> 於 2020年6月15日 週一 下午6:26寫道：

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***@***.**** commented on this gist. ------------------------------ Dear Shao Thanks a lot for your answers. It helped me a lot! Best wishes Aleksander Berentsen Prof. Dr. Aleksander Berentsen University of Basel Center for Innovative Finance Peter Merian-Weg 6 | Postfach | CH-4002 Basel | Switzerland Tel: +41 (0)61 207 12 67 | wwz.unibas.ch/en/berentsen<http://wwz.unibas.ch/en/berentsen> | www.cif.unibas.ch<http://www.cif.unibas.ch/> | www.blockchainbuch.de< http://www.blockchainbuch.de/> From: Tien Shao Ku ***@***.***> Sent: Dienstag, 9. Juni 2020 14:49 To: tienshaoku ***@***.***> Cc: Aleksander Berentsen ***@***.***>; Comment < ***@***.***> Subject: Re: tienshaoku/swap.js @tienshaoku commented on this gist. ________________________________ Hello Aleks, I use the ERC20 interface from openzeppelin: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol *require(Dai.transferFrom(msg.sender, address(this), _DaiAmount));Is this idea that I first send tokens from my metamask wallet to my contract? * -> Yep. As a reminder, before transferFrom(), you have to use the approve() function of the desired ERC20 (Dai in this example), so that you will not get an error while using transferFrom(). *Dai.approve(address(uniswapV2Router01), _DaiAmount);Is here the idea that I approve that the uniswap router spends these tokens after I have approved it? * -> You're right! Best regards, Shao alberentsen ***@***.******@***.***>> 於 2020年6月6日 週六 上午1:35寫道： > ***@***.**** commented on this gist. > ------------------------------ > > Hi Tien > I was looking for an example that uses swap.ExactTokensForETH so I found > you. I had no problem to replicate the function swapETHToDai() but the > function swapDaiForETH is not working. One reason is that you use the ERC20 > interface while I use the IERC20 interface from zeppelin. What ERC20 > interface do you use? > > I have also difficulty to figure out the meaning of: > > require(Dai.transferFrom(msg.sender, address(this), _DaiAmount)); > Is this idea that I first send tokens from my metamask wallet to my > contract? > > Dai.approve(address(uniswapV2Router01), _DaiAmount); > Is here the idea that I approve that the uniswap router spends these > tokens after I have approved it? > > As you can see I'm a beginner in solidity and I have very little > programming background. > Anyhow, it would be very helpful if you could help me in this matter. > > Best wishes > aleks > > — > You are receiving this because you authored the thread. > Reply to this email directly, view it on GitHub > < https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3331237>, > or unsubscribe > < https://github.com/notifications/unsubscribe-auth/AKV3KR3RCQCYABI3ZC5K7LTRVEUFJANCNFSM4NUNZ4FQ> > . > — You are receiving this because you commented. Reply to this email directly, view it on GitHub< https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3335673>, or unsubscribe< https://github.com/notifications/unsubscribe-auth/AF5N66WFCOGJ5MRDE32DW4TRVYVUFANCNFSM4NUNZ4FQ>. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3341968>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR43XME44WBFLX7O4YTRWXZODANCNFSM4NUNZ4FQ> .

I have indeed a question! Below you find to version of the same contract. The first one I learnt from you and the second would be a shortcut but I'm not sure whether I miss something.

pragma solidity ^0.5.0;
import "./IUniswapV2Router01.sol";

contract ExactEthForTokenV2 {
address internal constant UNISWAP_ROUTER_ADDRESS = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;

IUniswapV2Router01 public uniswaprouter;

constructor () public {
uniswaprouter = IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS);
    }

function swapETHToNBT() public payable {
address[] memory _paths = new address;
_paths[0] = WETHAddress;
_paths[1] = TokenAddress;
uniswaprouter.swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15);

//Question: Is there any benefit of doing it as you do:
//First, IUniswapV2Router01 public uniswaprouter;
//Second, uniswaprouter = IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS);
//Third, uniswaprouter.swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15);
//Is it also possible to use the Interface address directly (see the last line below) to call swapExactETHForTokens.

pragma solidity ^0.5.0;
import "./IUniswapV2Router01.sol";

contract ExactEthForTokenV2 {
address internal constant UNISWAP_ROUTER_ADDRESS = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;

constructor () public {
    }

function swapETHToNBT() public payable {
address[] memory _paths = new address;
_paths[0] = WETHAddress;
_paths[1] = TokenAddress;
IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS).swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15);

Dear Aleks, The two versions have the same functionality. The difference lies in the occasions. If the instance of IUniswapV2Router01 will be used multiple times in a smart contract, then we should declare it in the global scope as the first approach. By contrast, if you are sure that there will be only one function using the instance of IUniswapV2Router01, then the second approach is for sure cleaner. Shao alberentsen <notifications@github.com> 於 2020年6月16日 週二 下午5:50寫道：

…

***@***.**** commented on this gist. ------------------------------ I have indeed a question! Below you find to version of the same contract. The first one I learnt from you and the second would be a shortcut but I'm not sure whether I miss something. pragma solidity ^0.5.0; import "./IUniswapV2Router01.sol"; contract ExactEthForTokenV2 { address internal constant UNISWAP_ROUTER_ADDRESS = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D; IUniswapV2Router01 public uniswaprouter; constructor () public { uniswaprouter = IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS); } function swapETHToNBT() public payable { address[] memory _paths = new address <http://2>; _paths[0] = WETHAddress; _paths[1] = TokenAddress; uniswaprouter.swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15); //Question: Is there any benefit of doing it as you do: //First, IUniswapV2Router01 public uniswaprouter; //Second, uniswaprouter = IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS); //Third, uniswaprouter.swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15); //Is it also possible to use the Interface address directly (see the last line below) to call swapExactETHForTokens. pragma solidity ^0.5.0; import "./IUniswapV2Router01.sol"; contract ExactEthForTokenV2 { address internal constant UNISWAP_ROUTER_ADDRESS = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D; constructor () public { } function swapETHToNBT() public payable { address[] memory _paths = new address <http://2>; _paths[0] = WETHAddress; _paths[1] = TokenAddress; IUniswapV2Router01(UNISWAP_ROUTER_ADDRESS).swapExactETHForTokens.value(msg.value)(0, _paths, address(this), now + 15); — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3343219>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR324BM2EXFOADN6XHTRW455VANCNFSM4NUNZ4FQ> .

Hi Shao
I figured the problem out in the meantime.
Thanks again
aleks

Hi Aleks, Sorry for the late reply, as I have been quite busy recently. I happen to be majoring in Economics before, now in Computer Science :) I'm glad that you have solved it! But, allow me to paste this: https://github.com/Uniswap/uniswap-v1/blob/master/contracts/uniswap_exchange.vy You can find the source code of Uniswap V1 in its GitHub, and then deploy a copy of it on testnets so that you do not have to pay for anything! (Though it is in another smart contract language: Vyper. It's easier to understand than Solidity, but has far less attention and thus less documentation on the Internet.) Also, I think I do find the testnet address of smart contracts of Uniswap V1: *// mainnet const factory = '0xc0a47dFe034B400B47bDaD5FecDa2621de6c4d95' // testnets const ropsten = '0x9c83dCE8CA20E9aAF9D3efc003b2ea62aBC08351' const rinkeby = '0xf5D915570BC477f9B8D6C0E980aA81757A3AaC36' const kovan = '0xD3E51Ef092B2845f10401a0159B2B96e8B6c3D30' const görli = '0x6Ce570d02D73d4c384b46135E87f8C592A8c86dA' * They are hidden here: https://uniswap.org/docs/v1/frontend-integration/connect-to-uniswap/ In fact, most blockchain projects are open-source, so over 90% of the time, you can find the source code on Github. Additionally, there is actually a way to interact with Mainnet with some limitations: https://studydefi.com/testing-on-mainnet/ Feel free to ask! It's my pleasure to help more people get to know about blockchain and Ethereum :) I have actually written a Uniswap V2 coding tutorial, but it's in Chinese :( If you're interested, perhaps you can try to google translate it: https://medium.com/taipei-ethereum-meetup/uniswap-v2-implementation-and-combination-with-compound-262ff338efa Shao alberentsen <notifications@github.com> 於 2020年6月20日 週六 上午5:21寫道：

…

***@***.**** commented on this gist. ------------------------------ Hi Shao I figured the problem out in the meantime. Thanks again aleks — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3348021>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR5OQ53BUQQ2UPBYRA3RXPJEPANCNFSM4NUNZ4FQ> .

Hi Shao Thanks for all this. I will try it out! Best wishes aleks From: Tien Shao Ku <notifications@github.com> Sent: Sonntag, 21. Juni 2020 15:19 To: tienshaoku <tienshaoku@noreply.github.com> Cc: Aleksander Berentsen <aleksander.berentsen@unibas.ch>; Comment <comment@noreply.github.com> Subject: Re: tienshaoku/swap.js @tienshaoku commented on this gist.

________________________________ Hi Aleks, Sorry for the late reply, as I have been quite busy recently. I happen to be majoring in Economics before, now in Computer Science :) I'm glad that you have solved it! But, allow me to paste this: https://github.com/Uniswap/uniswap-v1/blob/master/contracts/uniswap_exchange.vy You can find the source code of Uniswap V1 in its GitHub, and then deploy a copy of it on testnets so that you do not have to pay for anything! (Though it is in another smart contract language: Vyper. It's easier to understand than Solidity, but has far less attention and thus less documentation on the Internet.) Also, I think I do find the testnet address of smart contracts of Uniswap V1: *// mainnet const factory = '0xc0a47dFe034B400B47bDaD5FecDa2621de6c4d95' // testnets const ropsten = '0x9c83dCE8CA20E9aAF9D3efc003b2ea62aBC08351' const rinkeby = '0xf5D915570BC477f9B8D6C0E980aA81757A3AaC36' const kovan = '0xD3E51Ef092B2845f10401a0159B2B96e8B6c3D30' const görli = '0x6Ce570d02D73d4c384b46135E87f8C592A8c86dA' * They are hidden here: https://uniswap.org/docs/v1/frontend-integration/connect-to-uniswap/ In fact, most blockchain projects are open-source, so over 90% of the time, you can find the source code on Github. Additionally, there is actually a way to interact with Mainnet with some limitations: https://studydefi.com/testing-on-mainnet/ Feel free to ask! It's my pleasure to help more people get to know about blockchain and Ethereum :) I have actually written a Uniswap V2 coding tutorial, but it's in Chinese :( If you're interested, perhaps you can try to google translate it: https://medium.com/taipei-ethereum-meetup/uniswap-v2-implementation-and-combination-with-compound-262ff338efa Shao alberentsen <notifications@github.com<mailto:notifications@github.com>> 於 2020年6月20日 週六 上午5:21寫道：

***@***.**** commented on this gist. ------------------------------ Hi Shao I figured the problem out in the meantime. Thanks again aleks — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3348021>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR5OQ53BUQQ2UPBYRA3RXPJEPANCNFSM4NUNZ4FQ> .

— You are receiving this because you commented. Reply to this email directly, view it on GitHub<https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3349431>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AF5N66QAR3UNDB3ZRXZNY33RXYCD3ANCNFSM4NUNZ4FQ>.

Hi Aleks, No problem :) Shao alberentsen <notifications@github.com> 於 2020年6月24日 週三 下午3:03寫道：

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***@***.**** commented on this gist. ------------------------------ Hi Shao Thanks for all this. I will try it out! Best wishes aleks From: Tien Shao Ku ***@***.***> Sent: Sonntag, 21. Juni 2020 15:19 To: tienshaoku ***@***.***> Cc: Aleksander Berentsen ***@***.***>; Comment < ***@***.***> Subject: Re: tienshaoku/swap.js @tienshaoku commented on this gist. ________________________________ Hi Aleks, Sorry for the late reply, as I have been quite busy recently. I happen to be majoring in Economics before, now in Computer Science :) I'm glad that you have solved it! But, allow me to paste this: https://github.com/Uniswap/uniswap-v1/blob/master/contracts/uniswap_exchange.vy You can find the source code of Uniswap V1 in its GitHub, and then deploy a copy of it on testnets so that you do not have to pay for anything! (Though it is in another smart contract language: Vyper. It's easier to understand than Solidity, but has far less attention and thus less documentation on the Internet.) Also, I think I do find the testnet address of smart contracts of Uniswap V1: *// mainnet const factory = '0xc0a47dFe034B400B47bDaD5FecDa2621de6c4d95' // testnets const ropsten = '0x9c83dCE8CA20E9aAF9D3efc003b2ea62aBC08351' const rinkeby = '0xf5D915570BC477f9B8D6C0E980aA81757A3AaC36' const kovan = '0xD3E51Ef092B2845f10401a0159B2B96e8B6c3D30' const görli = '0x6Ce570d02D73d4c384b46135E87f8C592A8c86dA' * They are hidden here: https://uniswap.org/docs/v1/frontend-integration/connect-to-uniswap/ In fact, most blockchain projects are open-source, so over 90% of the time, you can find the source code on Github. Additionally, there is actually a way to interact with Mainnet with some limitations: https://studydefi.com/testing-on-mainnet/ Feel free to ask! It's my pleasure to help more people get to know about blockchain and Ethereum :) I have actually written a Uniswap V2 coding tutorial, but it's in Chinese :( If you're interested, perhaps you can try to google translate it: https://medium.com/taipei-ethereum-meetup/uniswap-v2-implementation-and-combination-with-compound-262ff338efa Shao alberentsen ***@***.******@***.***>> 於 2020年6月20日 週六 上午5:21寫道： > ***@***.**** commented on this gist. > ------------------------------ > > Hi Shao > I figured the problem out in the meantime. > Thanks again > aleks > > — > You are receiving this because you were mentioned. > Reply to this email directly, view it on GitHub > < https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3348021>, > or unsubscribe > < https://github.com/notifications/unsubscribe-auth/AKV3KR5OQ53BUQQ2UPBYRA3RXPJEPANCNFSM4NUNZ4FQ> > . > — You are receiving this because you commented. Reply to this email directly, view it on GitHub< https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3349431>, or unsubscribe< https://github.com/notifications/unsubscribe-auth/AF5N66QAR3UNDB3ZRXZNY33RXYCD3ANCNFSM4NUNZ4FQ>. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/0d99ea04104f2e47f6b0b25d647a0d31#gistcomment-3352559>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AKV3KR3Y6KE37UWA6MNCEE3RYGQLPANCNFSM4NUNZ4FQ> .