Functions

Functions are typically called often, and should be one of your prime optimization focuses. Functions containing try-catch constructs are not optimizable, nor are functions containing other unpredictable constructs, like with or eval. If, for some reason, your function is not optimizable, keep its use to a minimum.

A very common optimization error involves the use of polymorphic functions. Functions that accept variable function arguments will be de-optimized. Avoid polymorphic functions.

An excellent explanation of how V8 performs speculative optimization can be found here: https://ponyfoo.com/articles/an-introduction-to-speculative-optimization-in-v8