What does complexity and scalability mean?

Question

Programming

Good afternoon, 2 words put me in a stupor:

1. Scalability
   
2. Complexity
   

What is scalable code?
For example, "the less nesting, the more scalable code" (even in the context of html it is used)

What does complexity mean?
For example "what do you know how to deal with complexity?"

Answer 1

What is scalable code?

This is code that is easy to "grow" - no shitty code, and as modular as it should be. As a rule, it means using the principles of SOLID. https://avivi.pro/blog/bud-solid/

What does complexity mean?

The best code is simple code. Readable. Where the ideas are so logical that they are understood by programmers of any level, and not just by a senior tomato.
How it's done - large procedures and methods are broken down into smaller ones, logically structuring the code. By making it "lightweight" and maintainable, it makes the task of debugging and scaling the code easier.

Answer 2

1. Scalability
2. Computational complexity

Answer 3

probably you need to check the if condition, and not assign attr to the element
https://jsfiddle.net/8L1ongeq/1/