# AxridToWeb3-Week9

By [2-333.eth](https://paragraph.com/@2-333.eth) · 2023-01-08

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**ENGLISH:**

*   **1、Currently we set**[**the token allowance is set to the max amount**](https://docs.alchemy.com/alchemy/road-to-web3/weekly-learning-challenges/9.-how-to-build-a-token-swap-dapp-with-0x-api#ii-set-the-approval-amount-to-maxapproval)**. Change this to be safer so the user only approves just the amount needed.**
    
    In the trySwap function, I adjusted the "MAXApproval" parameter to the number of tokens entered by the user in the front-end, using the "sellAmount" parameter in swapPriceJSON
    
    2、Show estimated gas in $
    
    First get "gasPrice" by using "getGasPrice" in Ethers:
    
    `provider.getGasPrice()`
    
    Then use Chainlink to get the "latestRoundData" data of ETH, in which the "answer" is the real-time price of ETH:
    
    `const addr = "0xD4a33860578De61DBAbDc8BFdb98FD742fA7028e" const priceFeed = new ethers.Contract(addr, aggregatorV3InterfaceABI, provider) priceFeed.latestRoundData() .then((roundData) => { ETHprice = roundData.answer.toString()/10e7// Do something with roundData console.log("Latest price", ETHprice) })`
    
    Finally, multiply estimatedGas, gasPrice, and ETHprice to get the $ gasfee:
    
    `ethers.utils.formatEther(swapPriceJSON.estimatedGas)*gasPrice.toString()*ETHprice`
    

After learning the basic syntax of js by myself, I successfully completed the transformation and upgrading of the basic code.

**Answer ALL of these questions:**

*   **Who are you, and what is your software development background?**
    
    I'm axrid, I'm not a computer science major, I only know some basic Python and JS. I'm learning solidity now and want to work in web3 related work.
    
*   **Why did you want to complete this lesson?**
    
    I taught myself the basic syntax of JS and wanted to consolidate what I learned in this lesson. So I built the code following the video tutorial and completed the challenge.
    
*   **When did you complete the project?**
    
    I started the course on November 1 and finished it on November 6, with a total duration of about 5h.
    
*   **What technologies did you use?**
    
    [https://docs.alchemy.com/docs/how-to-build-a-token-swap-dapp-with-0x-api](https://docs.alchemy.com/docs/how-to-build-a-token-swap-dapp-with-0x-api)
    
    I followed the official tutorials to learn, mainly using JS and the related APIs of Chainlink, 0x, and Alchemy.
    
*   **What did you enjoy about the tutorial?**
    
    Through learning and modifying the code, I understood the relationship between the front-end modules. I also understand that front-end and Solidity are equally important in Blockchain development.
    
*   **How do you think you can use this technology to build useful applications in the future? What are some specific example applications?**
    
    This is a tutorial about DEX, and to be honest, I'm not going to build a new DEX. in this lesson I learned to get token price through Chainink and interact with Blockchain through Ethers. I plan to make some JS scripts related to Blockchain.
    
*   **Who would you recommend this project to?**
    
    A friend of mine who has learned JS, C++, Python, maybe he can master this lesson easily.
    
*   **What is the Ethereum wallet address you would like to receive your PoK at?**
    
    My address (I may delete the wallet address from this post when I mint nft):
    
    0xe62ef3e82127bb97e641b15e866798c827206762
    
*   **My smart contract code:**
    
    [https://github.com/a9team2333/roadtoweb3/tree/main/week9](https://github.com/a9team2333/roadtoweb3/tree/main/week9)
    
*   **I completed the following two challenges:**
    
    **1、Currently we set**[**the token allowance is set to the max amount**](https://docs.alchemy.com/alchemy/road-to-web3/weekly-learning-challenges/9.-how-to-build-a-token-swap-dapp-with-0x-api#ii-set-the-approval-amount-to-maxapproval)**. Change this to be safer so the user only approves just the amount needed.**
    
    In the trySwap function, I adjusted the "MAXApproval" parameter to the number of tokens entered by the user in the front-end, using the "sellAmount" parameter in swapPriceJSON
    
    2、Show estimated gas in $
    
    First get "gasPrice" by using "getGasPrice" in Ethers:
    
    `provider.getGasPrice()`
    
    Then use Chainlink to get the "latestRoundData" data of ETH, in which the "answer" is the real-time price of ETH:
    
    `const addr = "0xD4a33860578De61DBAbDc8BFdb98FD742fA7028e" const priceFeed = new ethers.Contract(addr, aggregatorV3InterfaceABI, provider) priceFeed.latestRoundData() .then((roundData) => { ETHprice = roundData.answer.toString()/10e7// Do something with roundData console.log("Latest price", ETHprice) })`
    
    Finally, multiply estimatedGas, gasPrice, and ETHprice to get the $ gasfee:
    
    `ethers.utils.formatEther(swapPriceJSON.estimatedGas)*gasPrice.toString()*ETHprice`
    

![](https://storage.googleapis.com/papyrus_images/125886604e5c7af44bfc8e01974435fc.png)

中文:

自学了js的基本语法后，顺利的完成了基础代码的改造提升。

**answer ALL of these questions:**

*   **Who are you, and what is your software development background?**
    
    我是axrid，我不是计算机专业，只会一些基础的python和js。我现在正在学习solidity，想要从事web3相关的工作。
    
*   **Why did you want to complete this lesson?**
    
    我自学了js的基本语法，想要在这一课里巩固所学内容。因此我按照视频教程搭建了code，并完成了挑战。
    
*   **When did you complete the project?**
    
    我从11月1日开始学习，在11月6完成课程，总时长大概5h。
    
*   **What technologies did you use?**
    
    [https://docs.alchemy.com/docs/how-to-build-a-token-swap-dapp-with-0x-api](https://docs.alchemy.com/docs/how-to-build-a-token-swap-dapp-with-0x-api)
    
    我跟随官方教程进行学习，主要使用javascript，以及chainlink, 0x, alchemy
    
*   **What did you enjoy about the tutorial?**
    
    通过对代码的学习和修改，我理解了前端各个文件之间的关系。也明白了blockchain行业里，前端和solidity同样重要
    
*   **How do you think you can use this technology to build useful applications in the future? What are some specific example applications?**
    
    这是一个关于DEX的教程，老实说，我不会去搭建一个新的DEX。在这一课我学会了通过chainink获取token price，通过ethers与blockchain交互。我打算做一些与blockchain相关的js脚本。
    
*   **Who would you recommend this project to?**
    
    我的一位朋友，他学过js、c++、python，也许他可以很轻松的掌握这一课
    
*   **What is the Ethereum wallet address you would like to receive your PoK at?**
    
*   **My smart contract code:**
    
    [https://github.com/a9team2333/roadtoweb3/tree/main/week9](https://github.com/a9team2333/roadtoweb3/tree/main/week9)
    

我完成了以下两个挑战

1、目前我们设置令牌限额设置为最大金额.更改此项以使其更安全，以便用户仅批准所需的金额。

{}在trySwap中，我把MAXApproval的参数调整为用户在前端中输入的token数量，借用了swapPriceJSON中的sellAmount参数

2、以 $ 为单位显示估计的气体

{}首先通过Ethers中的getGasPrice来获取gasPrice

`provider.getGasPrice()`

然后使用Chainlink来获取ETH的latestRoundData数据，里面的”answer”就是ETH的实时价格

`const addr = "0xD4a33860578De61DBAbDc8BFdb98FD742fA7028e" const priceFeed = new ethers.Contract(addr, aggregatorV3InterfaceABI, provider) priceFeed.latestRoundData() .then((roundData) => { ETHprice = roundData.answer.toString()/10e7// Do something with roundData console.log("Latest price", ETHprice) })`

最终将estimatedGas、gasPrice、ETHprice相乘，得到以美元计价的gasfee

`ethers.utils.formatEther(swapPriceJSON.estimatedGas)*gasPrice.toString()*ETHprice`

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*Originally published on [2-333.eth](https://paragraph.com/@2-333.eth/axridtoweb3-week9)*