refactor: replace var statements

[Fdawgs]

See fastify/fastify#5756

Benchmarks:

> [email protected] bench
> node ./benchmark/bench.js

short string............................................. x 31,349,530 ops/sec ±0.31% (193 runs sampled)
unsafe short string...................................... x 1,802,803,481 ops/sec ±0.10% (194 runs sampled)
short string with double quote........................... x 19,272,037 ops/sec ±0.24% (193 runs sampled)
long string without double quotes........................ x 15,877 ops/sec ±0.15% (196 runs sampled)
unsafe long string without double quotes................. x 1,805,311,324 ops/sec ±0.09% (196 runs sampled)
long string.............................................. x 14,947 ops/sec ±0.25% (195 runs sampled)
unsafe long string....................................... x 1,806,650,421 ops/sec ±0.10% (196 runs sampled)
number................................................... x 1,804,422,038 ops/sec ±0.14% (196 runs sampled)
integer.................................................. x 267,442,465 ops/sec ±0.13% (195 runs sampled)
formatted date-time...................................... x 1,418,094 ops/sec ±0.20% (195 runs sampled)
formatted date........................................... x 1,184,518 ops/sec ±0.24% (194 runs sampled)
formatted time........................................... x 1,164,235 ops/sec ±1.76% (191 runs sampled)
short array of numbers................................... x 76,988 ops/sec ±3.13% (176 runs sampled)
short array of integers.................................. x 107,147 ops/sec ±0.46% (192 runs sampled)
short array of short strings............................. x 27,265 ops/sec ±0.24% (193 runs sampled)
short array of long strings.............................. x 27,155 ops/sec ±0.20% (189 runs sampled)
short array of objects with properties of different types x 14,711 ops/sec ±0.29% (193 runs sampled)
object with number property.............................. x 1,801,200,799 ops/sec ±0.09% (196 runs sampled)
object with integer property............................. x 269,369,444 ops/sec ±0.11% (196 runs sampled)
object with short string property........................ x 31,059,097 ops/sec ±0.26% (193 runs sampled)
object with long string property......................... x 15,142 ops/sec ±0.14% (196 runs sampled)
object with properties of different types................ x 3,061,414 ops/sec ±0.26% (194 runs sampled)
simple object............................................ x 14,934,076 ops/sec ±0.30% (191 runs sampled)
simple object with required fields....................... x 15,324,092 ops/sec ±0.23% (194 runs sampled)
object with const string property........................ x 1,789,865,450 ops/sec ±0.18% (195 runs sampled)
object with const number property........................ x 1,796,809,786 ops/sec ±0.14% (196 runs sampled)
object with const bool property.......................... x 1,763,976,530 ops/sec ±0.46% (194 runs sampled)
object with const object property........................ x 1,759,086,849 ops/sec ±0.21% (193 runs sampled)
object with const null property.......................... x 1,768,421,296 ops/sec ±0.16% (192 runs sampled)

Checking out "master"
Execute "npm run bench"

> [email protected] bench
> node ./benchmark/bench.js

short string............................................. x 23,912,633 ops/sec ±3.26% (189 runs sampled)
unsafe short string...................................... x 1,774,499,751 ops/sec ±0.18% (195 runs sampled)
short string with double quote........................... x 18,989,670 ops/sec ±0.24% (193 runs sampled)
long string without double quotes........................ x 15,537 ops/sec ±0.21% (194 runs sampled)
unsafe long string without double quotes................. x 1,778,937,405 ops/sec ±0.17% (194 runs sampled)
long string.............................................. x 14,970 ops/sec ±0.18% (193 runs sampled)
unsafe long string....................................... x 1,780,989,200 ops/sec ±0.29% (194 runs sampled)
number................................................... x 1,800,349,688 ops/sec ±0.24% (195 runs sampled)
integer.................................................. x 268,647,172 ops/sec ±0.22% (194 runs sampled)
formatted date-time...................................... x 1,415,994 ops/sec ±0.26% (196 runs sampled)
formatted date........................................... x 1,194,071 ops/sec ±0.21% (195 runs sampled)
formatted time........................................... x 1,191,121 ops/sec ±0.24% (195 runs sampled)
short array of numbers................................... x 118,071 ops/sec ±0.65% (191 runs sampled)
short array of integers.................................. x 117,691 ops/sec ±0.39% (193 runs sampled)
short array of short strings............................. x 27,034 ops/sec ±0.25% (186 runs sampled)
short array of long strings.............................. x 27,887 ops/sec ±0.24% (192 runs sampled)
short array of objects with properties of different types x 14,225 ops/sec ±1.26% (186 runs sampled)
object with number property.............................. x 1,386,347,717 ops/sec ±2.64% (177 runs sampled)
object with integer property............................. x 268,999,488 ops/sec ±0.18% (196 runs sampled)
object with short string property........................ x 31,696,967 ops/sec ±0.22% (193 runs sampled)
object with long string property......................... x 14,956 ops/sec ±0.17% (195 runs sampled)
object with properties of different types................ x 3,339,428 ops/sec ±0.25% (194 runs sampled)
simple object............................................ x 15,121,786 ops/sec ±0.24% (194 runs sampled)
simple object with required fields....................... x 15,377,960 ops/sec ±0.27% (194 runs sampled)
object with const string property........................ x 1,805,443,865 ops/sec ±0.08% (195 runs sampled)
object with const number property........................ x 1,797,637,123 ops/sec ±0.16% (192 runs sampled)
object with const bool property.......................... x 1,799,121,125 ops/sec ±0.13% (193 runs sampled)
object with const object property........................ x 1,806,433,745 ops/sec ±0.10% (195 runs sampled)
object with const null property.......................... x 1,793,772,787 ops/sec ±0.21% (195 runs sampled)

short string..............................................+31.1%
unsafe short string........................................+1.6%
short string with double quote............................+1.49%
long string without double quotes.........................+2.19%
unsafe long string without double quotes..................+1.48%
long string...............................................-0.15%
unsafe long string........................................+1.44%
number....................................................+0.23%
integer...................................................-0.45%
formatted date-time.......................................+0.15%
formatted date.............................................-0.8%
formatted time............................................-2.26%
short array of numbers....................................-34.8%
short array of integers...................................-8.96%
short array of short strings..............................+0.85%
short array of long strings...............................-2.62%
short array of objects with properties of different types.+3.42%
object with number property..............................+29.92%
object with integer property..............................+0.14%
object with short string property.........................-2.01%
object with long string property..........................+1.24%
object with properties of different types.................-8.33%
simple object.............................................-1.24%
simple object with required fields........................-0.35%
object with const string property.........................-0.86%
object with const number property.........................-0.05%
object with const bool property...........................-1.95%
object with const object property.........................-2.62%
object with const null property...........................-1.41%
Back to ref/var 3979ddd

Checklist

• run npm run test and npm run benchmark
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm