sueboy: javascript

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程式設計師是如何神不知鬼不覺的弄丟銀行1分錢的?

https://kknews.cc/zh-tw/finance/zpxln2q.html

[開發經驗分享][JavaScript]浮點數運算出現一堆小數位數

https://dotblogs.com.tw/WillianHsiaoDotNetBLog/2020/01/15/JavascriptFloatCaculateBug?fbclid=IwAR0SnYG7FnesbfENWCsOT_ceGxqab6Q1dksJ3qIr-pe65m55wNBlWLc0Ns0

精確的浮點數運算 ?

https://medium.com/pyladies-taiwan/%E7%B2%BE%E7%A2%BA%E7%9A%84%E6%B5%AE%E9%BB%9E%E6%95%B8%E9%81%8B%E7%AE%97-28d34e652e51

javascript How does the double exclamation (!!) work in javascript?

https://stackoverflow.com/questions/784929/what-is-the-not-not-operator-in-javascript

https://stackoverflow.com/questions/29312123/how-does-the-double-exclamation-work-in-javascript

value	!value	!!value
false	true	false
true	false	true
null	true	false
undefined	true	false
0	true	false
-0	true	false
1	false	true
-5	false	true
NaN	true	false
''	true	false
'hello'	true	false

javascript functions parm default value

https://stackoverflow.com/questions/6600868/set-default-value-of-javascript-object-attributes


// default num: 0, unit: 'pics'
function items(op) {
  const { num, unit } = Object.assign({}, { num: 0, unit: 'pics'}, op);
}

[轉]140 favorite JavaScript utilities in single line of code! No more!

https://1loc.dev/

javascript firestore object sort


  const bookListsQuery = await modules.firestore.collection('books')
    .get();

  const sortedObj = Object.values(bookListsQuery.docs).sort(function(a, b){
    console.log('a %s  b %s', a.data().order, b.data().order)
    return Number(a.data().order) > Number(b.data().order);
  });
        
  sortedObj.forEach(function(doc){
    console.log(doc.data())
  });

other way

object use map to array, then it sorted.


  const bookListsQuery = await modules.firestore.collection('books')
    .get();

  const sortedArr = bookListsQuery.docs.map(function (doc) {  // 轉換成array
    return doc.data()
  });

  sortedArr.sort(function compare(a, b) {
     return a.order > b.order; // 升 小->大
  });

  sortedArr.forEach(function(data){
    console.log(data.data())
  })

==========

Sorting multiple object properties with JavaScript

https://bithacker.dev/javascript-object-multi-property-sort


let students = [{
  firstName: 'John',
  lastName: 'Appletree',
  grade: 12
},{
  firstName: 'Mighty',
  lastName: 'Peachtree',
  grade: 10
},{
  firstName: 'Kim',
  lastName: 'Appletree',
  grade: 11
},{
  firstName: 'Shooter',
  lastName: 'Appletree',
  grade: 12
}];


let sortBy = [{
  prop:'grade',
  direction: -1
},{
  prop:'lastName',
  direction: 1
}];


array.sort(function(a,b){
  let i = 0, result = 0;
  while(i < sortBy.length && result === 0) {
    result = sortBy[i].direction*(a[ sortBy[i].prop ].toString() < b[ sortBy[i].prop ].toString() ? -1 : (a[ sortBy[i].prop ].toString() > b[ sortBy[i].prop ].toString() ? 1 : 0));
    i++;
  }
  return result;
})

javascript console.log object

console.log('show value string, object %s %O', var.string, var.object);

async getaaa()
async getbbb()
async getccc()

=======new way=======
async refreshall(){

await Promise.all( xxxxxx.map(async (value, index) =>{
aaa = await getaaa()
}))

await Promise.all( xxxxxx.map(async (value, index) =>{
bbb = await getbbb()

}))

await Promise.all( xxxxxx.map(async (value, index) =>{

ccc = await getccc()

}))

}

=======old way=======
async refreshall(){

await Promise.all( xxxxxx.map(async (value, index) =>{
aaa = await getaaa()
bbb = await getbbb()
ccc = await getccc()

}))

}

1. map usually return something, here just throw
2. if use foreach(), get error. Like foreach is not function, can't async await.

old way aaa order is good, but bbb ccc order is bad.
new way all aaa bbb ccc order is ok.

call by value call by reference object array push

Problem：
array A
A.push(item)
item is object from for or map or foreach....etc

show A all add item is same.......

Solve：

var txxxxx = [] // xxxx is any word

=====loop start=====
txxxx[index] = item //index is from for or map or foreach...etc

ot = {
xxxx: txxxx[index]
}

A.push(ot)
=====loop end=====

[轉]async 、 await es6 promise javqscript

https://hackmd.io/s/Bko9gUGYZ

[轉]在 JavaScript 棄用 For 迴圈，擁抱 Reduce、ForEach、Filter、Map

https://yami.io/reduce-foreach-filter-map/

Preloading images and executing code only after all images have loaded

http://www.javascriptkit.com/javatutors/preloadimagesplus.shtml

http://fragged.org/preloading-images-using-javascript-the-right-way-and-without-frameworks_744.html

[轉]jQuery 之 checkbox 及 radio 設定值的

http://note.tc.edu.tw/175.html

[radio 取值]

以下範例示範當使用者按下 submit ( id=sb1 ) 時的檢查動作，其中 radio 的 name=doway

$("#sb1").click(function(){
var method =$("input[name='doway']:checked").val(); //radio 取值，注意寫法
if( typeof(method) == "undefined"){ // 注意檢查完全沒有選取的寫法，這行是精華
alert( "請選取操作方式！");
return false;
}

[轉]不會不專業！只要懂這五題你就是 Pro 級的 JavaScript 工程師

http://buzzorange.com/techorange/2015/08/18/humans-create-softwarehow-do-you-judge-a-javascript-programmer-by-only-5-questions/

Q1：你能解釋出什麼是 apply 函數嗎？

當之後你在建立 Library 時你一定要記得最常使用的 apply 函數

Q2：你能跟我解釋一下什麼是 map 嗎？不仿就再問問有關 reduce 方法。如果你不懂什麼是 map ，這代表著你在功能性撰寫程式程度是零！但千萬別放棄治療，建議你從這快開始你的學習之旅：A dirt simple introduction to higher order functions in JavaScript.

Q3：能解釋什麼是 bind 嗎？
Q4：解釋一下什麼是 closures ？

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