Reusing a Last Assignment
Explore how to use the useMemo hook in React to boost application performance by reusing the last assigned value. Understand the effects of different dependency arrays, how useMemo manages various value types, and the distinction between useMemo and React updates. This lesson equips you to apply useMemo effectively for caching calculations and enhancing efficiency in React components.
Leveraging useMemo for optimal performance
Reusing a value and memorizing a value sometimes refer to similar behavior. However, it's worth noting that the useMemo hook can only remember one value from the past, the last value.
A single JavaScript variable, by default, serves a purpose that, unless overwritten by a new assignment, holds the previously assigned value. So, take caution when reading the word "memo" here.
Have you considered interpreting the term “memo” not as the act of memorizing all values but rather as representing a single value, aligning with React’s intended design? Have you explored classical memorization?
How useMemo reuses the previous assignment is controlled by a deps dependency array, and it uses the areDepsEqual utility function to compare two dependency arrays between the previous and current updates. We will skip the source code here and jump straight to the scenarios that correspond to each dependency array configuration.
Similarly, we get three cases here, no dependency, empty dependency, and some dependencies: