Javascript

Split regex

1: when using split function using regex, if we want to include delimiters in array instead of just skipping them then we need to include brackets for delimiters. for eg:
```
calcInput='2*3'
 let arr = calcInput.split(/([*\/+-])/); 
// arr-> ['2', '*', '3']
without brackets split(/[*\/+-])/)
// arr=['2', '3']
```

2: typeof: to get type of literal.

for eg:

typeof 'str’ -> ‘string’

regex reference

JavaScript RegExp Reference

 import re
In [14]: par  = "This is a paragraph? So it is! Ok, there are 3 sentences."
In [15]: re.split(r'[.!?]+', par)
Out[15]: ['This is a paragraph', ' So it is', ' Ok, there are 3 sentences', '']

for splitting sentences in python

Parsing using regex

Suppose if we wnna extract id from url or text then

id = /var k__id = "(.*?)"/.exec(result)[1]

also to extract id from embed youtube video.

for eg:

let url="[https://www.youtube.com/embed/Ko58_KjgM0E](https://www.youtube.com/embed/Ko58_KjgM0E)" 
let reg=/embed\/(.*)/
const id=reg.exec('https://www.youtube.com/embed/Ko58_KjgM0E')[1]

// Output:
// "Ko58_KjgM0E"

Using fetch to send form data

in body use format <key>=<value> and use content-type: "application/x-www-form-urlencoded".

const getToken = async () => {
    const url = "https://accounts.spotify.com/api/token";
    const authOptions = {
      method: "post",
      // url: "https://accounts.spotify.com/api/token",
      headers: {
        Authorization:
          "Basic " +
          new Buffer(clientID + ":" + clientSecret).toString("base64"),
        "Content-Type": "application/x-www-form-urlencoded",
      },
			// form data with key 'grant_type' and value 'client_credentials'
			// written as
      body: "grant_type=client_credentials",

      // json: true,
    };

    const result = await fetch(url, authOptions);
    const data = await result.json();
    return data.access_token;
  };

HTTP basics

https://eloquentjavascript.net/18_http.html

onchange on select element

Another approach which can be handy in some situations, is passing the value of the selected <option /> directly to the function like this:

function myFunction(chosen) {
  console.log(chosen);
}

<select onChange="myFunction(this.options[this.selectedIndex].value)">
  <option value="1">Text 1</option>
  <option value="2">Text 2</option>
</select>

for react

 <select
      onChange={(e) =>
        myFunction(e.target.options[e.target.selectedIndex].value)
      }

Stimulate ctrl+click event

https://stackoverflow.com/questions/34255506/simulate-ctrl-click-with-javascript-or-jquery-to-open-a-new-tab-without-focus

In pure javascript, you can use the [MouseEvent](https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/MouseEvent) for that:
```
document.getElementById("todo").dispatchEvent(new MouseEvent("click", {ctrlKey: true}));
```
To programatically open a new tab you can do that:
```
const a = document.createElement("a");
a.setAttribute("href", "https://www.google.com/");
a.dispatchEvent(new MouseEvent("click", {ctrlKey: true}));
```

Local storage

const notestring = localStorage.getItem("notes");

// we can store objects so we need to convert them in json string first
const arrString = JSON.stringify(notes);
localStorage.setItem("notes", arrString);
// here 'notes' is key and arrString is value

// to remove the key
localStorage.removeItem("notes");

Use npm package in vanilla js

install browserify using

npm install -g browserify

then install npm package in same directory

npm i js-crypto-rsa

script.js
```
const rsa=require('js-crypto-rsa')

const key=rsa.generateKey(2048)
```
finally use

browserify script.js -o bundle.js

in index.html

<script src="bundle.js"></script>

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