Examining JavaScript code optimized for a performance-sensitive environment, specifically a game engine in mobile settings.
Oftentimes, this code avoids using local variables and instead relies on explicit chains, such as:
if (this.x.y[z].i) {
this.x.y[z].a += this.x.y[z].b;
}
In cases where both this.x.y and this.x.y.z indicate "duplication," without getters for intermediate properties, and with q as a locally unused variable, the following semantic equivalence can be considered.
var q = this.x.y[z]
if (q.i) {
q.a += q.b;
}
(Names are kept generic to minimize bias; focus is not on which "pattern" to follow - although the latter is preferred here.)
Before delving into comments about coding for clarity and avoiding premature optimization, consider the following!
Given the assertions/axioms below, and clarifying that the issue at hand is not performance improvement but rather potential performance decline related to using local cache/"alias" variables in relevant JavaScript implementations:
- Introducing a local variable for frequently accessed members enhances code readability. (Subjective, yet assumed true for this discussion)
- Using a local variable for non-dynamic properties assures consistent semantics.
- No closures are created over local variables, eliminating concerns regarding object lifetime or larger execution context scope.
- Focus lies on mobile browsers, including non/low-JIT versions like JavaScriptCore and pre-V8 Android engines.
- Browsers are well-optimized for this scenario, so any performance increase due to utilizing local variables is unlikely - opposite of the concern here.
Could employing local variables instead of direct property access result in a noticeable loss in performance? In situations where the decline is "non-negligible?"