In JavaScript, what's the most performant way to determine the first character in a string: startsWith, charAt, or [0]

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While writing some code that needs to be as performant as possible, I came across this question about charAt vs startsWith, but then realized it applied specifically to Java. After running some tests on jsperf.com, I found my answer. See below.

javascript
1 Answers

tl;dr

In Chrome 102, startsWith is faster than charAt. [0] is somewhere in the middle.

perf.link Results

You can view the perf.link test here. Below are the results I got testing in Chrome Version 102.0.5005.115 (Official Build) (arm64) / macOS Monterey Version 12.4:

Setup code:

const strs = [
  '',
  '*',
  '#',
  '*short',
  '#short',
  '*'.padEnd(2500, '-'),
  '#'.padEnd(2500, '-'),
]

startsWith

strs.forEach(str => str.startsWith('*'))
// 1,521,590 ops/s
// fastest

charAt

strs.forEach(str => str.charAt(0) === '*')
// 1,060,830 ops/s

[0]

strs.forEach(str => str[0] === '*')
// 1,294,190 ops/s
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