HTML <meta> http-equiv Attribute

The http-equiv attribute provides an HTTP header for the information/value of the content attribute.

The http-equiv attribute can be used to simulate an HTTP response header.

X-UA-Compatible is a document mode meta tag that allows web authors to choose what version of Internet Explorer the page should be rendered as. It is used by Internet Explorer 8 to specify whether a page should be rendered as IE 7 (compatibility view) or IE 8 (standards view).

The href attribute specifies the URL of the page the link goes to.

If the href attribute is not present, the <a> tag will not…

Why do I need Keys in React Lists?

There can be thousands of lists in an app and It could take a toll on the application’s performance. To optimize and improve performance aspect, React uses an unique key to identify which item has changed-modify, add, remove.
You should assign an unique key for each item instead of using an index as a key because an index can be changed as you add/remove elements. When you use index as a key and add a new element into an array, old index is used when you render. It creates unwanted behavior.
It’s not recommend to use an index instead of generating…

  1. Error 400: invalid_request
    Google: Permission denied to generate login hint
  2. “Not a valid origin for the client: http://127.0.0.…egister this origin for your project’s client ID.”
  3. The source list for Content Security Policy directive ‘script-src’ contains an invalid source: ‘’strict-dynamic’’. It will be ignored.

For the number 1 and 2, you should check ‘ Authorized Javascript Origins’ url. You can not use the numeric url( here, so change that url to ‘localhost:8080’.
To get this url, use the command ‘npx ngrok http 8080’ on your console.

For the number 3 error, you should check if you’re using the safari. It is not an error but a warning that your browser does not support the ‘strict-dynamic’ token.

AND clean the cache/cookie.

Strict mode

Strict mode is a special mode that user can activate in JS which makes it easier for us to write a secure JS code.
All user needs to activate this strict mode is to write this at the beginning of the script.
‘use strict’;
Without strict mode, JS will fail silently without letting user know that there is a mistake.

Function declarations vs Expressions

Just like a variable starts with ‘var/let /const’, function declaration also should begin with ‘function’ and it is used as function name to invoke the function.

function age1(year) {return 2020-year;}

Function expression is stored in a variable.


I wanted to take a full stack web course in Udacity and in order to start, I should be able to write codes with object oriented language. Since I’ve only studied C language, I decided to take JS course in Udemy beforehand.

3 ways of variable declaration — var, let, const

1. Var
Var can be re-declared later and it is also mutable. However, It is not good practice to use this and leave a potential to create a bug later. Var is old way of declaring variable so that it is not used as often.

2. Let
Let is used to declare any types of variables such as number…


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