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perf(webidl): check ByteString code units with a native scan #5903

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zirkelc wants to merge 1 commit into from
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perf(webidl): check ByteString code units with a native scan #5903

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18 changes: 11 additions & 7 deletions lib/web/webidl/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -607,6 +607,9 @@ webidl.converters.DOMString = function (V, prefix, argument, flags) {
return String(V)
}

// Matches any UTF-16 code unit above 255.
const nonByteStringCodeUnit = /[\u0100-\uffff]/

// https://webidl.spec.whatwg.org/#es-ByteString
webidl.converters.ByteString = function (V, prefix, argument) {
// 1. Let x be ? ToString(V).
Expand All @@ -621,13 +624,14 @@ webidl.converters.ByteString = function (V, prefix, argument) {

// 2. If the value of any element of x is greater than
// 255, then throw a TypeError.
for (let index = 0; index < x.length; index++) {
if (x.charCodeAt(index) > 255) {
throw new TypeError(
'Cannot convert argument to a ByteString because the character at ' +
`index ${index} has a value of ${x.charCodeAt(index)} which is greater than 255.`
)
}
// Note: A native regular expression scan instead of a loop over x. The
// index is only needed for the error message.
if (nonByteStringCodeUnit.test(x)) {
const index = x.search(nonByteStringCodeUnit)
throw new TypeError(
'Cannot convert argument to a ByteString because the character at ' +
`index ${index} has a value of ${x.charCodeAt(index)} which is greater than 255.`
)
}

// 3. Return an IDL ByteString value whose length is the
Expand Down