google/closure-compiler

String.fromCharCode optimization

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#3,606 opened on May 27, 2020

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P4featgood first issue

Description

I used: https://closure-compiler.appspot.com/home

Input code: document.write(String.fromCharCode(115));

Expected output: document.write("s")

Actual output: document.write(String.fromCharCode(115));

I expected the String.fromCharCode function to be removed to just the resulting character.

Contributor guide

Tech stack
javascript
Domain
performance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaJavaScriptAST manipulationoptimization passes
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the existing peephole optimization passes in the Closure Compiler, particularly the 'PeepholeOptimizations' class that handles constant folding. Look for patterns where function calls with constant arguments are replaced with the result. For String.fromCharCode with a single numeric argument, the optimization should replace it with the corresponding character string. Check the existing tests in the 'test' directory for similar optimizations to understand the required test structure. Consider examining the 'ProcessClosurePrimitives' or 'ReplaceStrings' passes for relevant logic.