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Even faster array parsing #20

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Merged
merged 2 commits into from
Mar 6, 2025
Merged

Even faster array parsing #20

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a7dfb98
String accumulation is faster than array join
benjie Mar 6, 2025
0f5cca5
No measurable performance difference and simpler code
benjie Mar 6, 2025
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29 changes: 13 additions & 16 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,14 @@ const NULL_STRING = 'NULL'
function makeParseArrayWithTransform (transform) {
const haveTransform = transform != null
return function parseArray (str) {
const rbraceIndex = str.length - 1
if (rbraceIndex === 1) {
return []
}
if (str[rbraceIndex] !== RBRACE) {
throw new Error('Invalid array text - must end with }')
}

// If starts with `[`, it is specifying the index boundas. Skip past first `=`.
let position = 0
if (str[position] === LBRACKET) {
Expand All @@ -29,17 +37,12 @@ function makeParseArrayWithTransform (transform) {
if (str[position++] !== LBRACE) {
throw new Error('Invalid array text - must start with {')
}
const rbraceIndex = str.length - 1
if (str[rbraceIndex] !== RBRACE) {
throw new Error('Invalid array text - must end with }')
}
const output = []
let current = output
const stack = []

let currentStringStart = position
const currentStringParts = []
let hasStringParts = false
let currentString = ''
let expectValue = true

for (; position < rbraceIndex; ++position) {
Expand All @@ -56,8 +59,7 @@ function makeParseArrayWithTransform (transform) {
while (backSlash !== -1 && backSlash < dquot) {
position = backSlash
const part = str.slice(currentStringStart, position)
currentStringParts.push(part)
hasStringParts = true
currentString += part
currentStringStart = ++position
if (dquot === position++) {
// This was an escaped doublequote; find the next one!
Expand All @@ -68,14 +70,9 @@ function makeParseArrayWithTransform (transform) {
}
position = dquot
const part = str.slice(currentStringStart, position)
if (hasStringParts) {
const final = currentStringParts.join('') + part
current.push(haveTransform ? transform(final) : final)
currentStringParts.length = 0
hasStringParts = false
} else {
current.push(haveTransform ? transform(part) : part)
}
currentString += part
current.push(haveTransform ? transform(currentString) : currentString)
currentString = ''
expectValue = false
} else if (char === LBRACE) {
const newArray = []
Expand Down