there is no hard and fast rule for this. in general think of it like if you haven't heard of it mark yourself 0. read about it a little and make it 1. theory knowledge is enough to rate yourself upto 3.
you need to have some experience to rate yourself about 4.
for the skills, let us take javascript as an example.
10 - top 2 percent in the world, i write libraries on my own.
9 - I know event life cycle, i can pick up any javascript based framework in 2 days
8 - i know about promises, async await, i can write decent code, i can debug
7 - i know how to get the work done in javascript but i don't know the inner workings
6 - i know about javasript and node js. i know i can use it across the projects
5 - i know about modules and dependency, i can make use of plugins, i had worked on jquery
4 - i can write basic code in javascript
3 - i know enough about javascript but have no hands on coding experience
2 - javascript can do some interactions on browser
1 - what is javascript? is it similar to java?
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