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JavaScript

  • comparisons of different libraries & frameworks
    • https://todomvc.com/

jQuery

to include jQuery

<head>
  <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
</head>

basics

declaration

  • var
  • let
    • block scoped
  • const
    • block scoped
    • can't change value

for loop

  • for(let i=0; i<=s.length; i++)
    • 千萬要加 let
  • for(var item of array) = for item in array in Python
  • for(var i in array) = for i in range(len(array)) in Python
  • for(var key in json) = for key in dict in Python

string

slice

str.slice(0,5)

function

execute function after another

example 

# func1 -> func2
function func1(something, callback){
    console.log(something);
    callback();
}
function func2(something){
    console.log(something);
}
func1('haha', func2);

pass parameter to callback

example 

function funcHandler(callback){
    callback(function(){
        console.log('2nd');
    });
}
function func1(something, callback){
    console.log(something);
    callback();
}
funcHandler(function(callback){
    func1('1st', callback);
});
// result: 
// '1st'
// '2nd'

https://stackoverflow.com/a/3458816/15493213

event handler

$(document).off("change","[name=refundItem]");
$(document).on("change", "[name=refundItem]", function(){
  itemidx = this.value;
  if(this.checked){
    $('#refundAmt'+itemidx).show();
  }
  if(!this.checked){
    $('#refundAmt'+itemidx).hide();
  }
});

$('#refresh').off('click');
$('#refresh').on('click', function(){
  console.log('fwfw');
  getOverallAttendance();
});

https://stackoverflow.com/questions/10979865

When setting a cookie on the child page / subdomain that has been set in root page / main domain, it will create a duplicate cookie in front of the previous one, instead of directly changing the value. To avoid this, append domain & path when setting cookie.

document.cookie = cookieName + "=" + newValue + '; domain=' + window.location.hostname + '; path=/';

https://stackoverflow.com/a/5671466/15493213

disable/enable style

jQuery 

$('#your_style').get(0).type = 'text' //diable
$('#your_style').get(0).type = '' //enable

https://stackoverflow.com/questions/5609165/changing-attribute-type-from-text-to-password

vanilla https://stackoverflow.com/questions/54440748/how-to-disable-a-style-element-in-html-js

HTTP Request

Axios

axios({
  method: 'post',
  url: '/login',
  data: {
    firstName: 'Finn',
    lastName: 'Williams'
  }
});

axios.post('/login', {
  firstName: 'Finn',
  lastName: 'Williams'
})
.then((response) => {
  console.log(response);
}, (error) => {
  console.log(error);
});

change theme

Use data attribute.

e.g.

function toggleTheme(){
  prevTheme = document.documentElement.dataset.theme;
  document.documentElement.dataset.theme = prevTheme === "night" ? "day" : "night"; 
}

:root {
  --color-bg: #000;
  --color-txt: #fff;
}
:root[data-theme="day"] {
  --color-bg: #fff;
  --color-txt: #000;
}
body {
  background: var(--color-bg);
  color: var(--color-txt);
}

ref

Make html directly editable

document.body.contentEditable=true

draggable element

https://jsfiddle.net/dlccyes/s84thyLn/2/

using jquery drag #night-btn in this code 

var initPos = [-1,-1];
$('#night-btn').click(function(e){
    if(e.clientX == initPos[0] && e.clientY == initPos[1]){
        if(!night){
            $('#day-css').remove();
            $('head').append('<link rel="stylesheet" href="style_b.css" id="night-css">');
            $('#night-btn').html('🌞');
            night = 1;
        }else{
            $('#night-css').remove();
            $('head').append('<link rel="stylesheet" href="style_w.css" id="day-css">');
            $('#night-btn').html('🌚');
            night = 0;
        }
    }
});

$('#night-btn').mousedown(function(e){
    initPos = [e.clientX, e.clientY];
    yoffset = $('#night-btn').offset().top-e.clientY;
    xoffset = $('#night-btn').offset().left-e.clientX;
    onmousemove = function(e){
        yy = yoffset+e.clientY;
        xx = xoffset+e.clientX
        $("#night-btn").css({top: yy, left: xx, position:'absolute'});
    };
});
$('#night-btn').mouseup(function(e){
    onmousemove = function(){};
});