Custom scope implementation: Reasoning

[Flamefire]

I'm interested in why the custom scope implementation was done and what exactly it does. There are other scope-resolving implementations (e.g. escope) which could be used instead. Why are they not?

[wisec]

• performances, as all those esprima/etraverse plugin execute AST from scratch.
• we need more descriptive data struct, such as name-value pairs, object prototype stuff and more