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Implement String.fromCharCode #1619

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Oct 4, 2021
Merged

Implement String.fromCharCode #1619

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30 changes: 30 additions & 0 deletions boa/src/builtins/string/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,7 @@ impl BuiltIn for String {
.name(Self::NAME)
.length(Self::LENGTH)
.property("length", 0, attribute)
.static_method(Self::from_char_code, "fromCharCode", 1)
.method(Self::char_at, "charAt", 1)
.method(Self::char_code_at, "charCodeAt", 1)
.method(Self::code_point_at, "codePointAt", 1)
Expand Down Expand Up @@ -240,6 +241,35 @@ impl String {
Err(context.construct_type_error("'this' is not a string"))
}

/// `String.fromCharCode(...codePoints)`
///
/// Construct a `String` from one or more code points (as numbers).
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/multipage/text-processing.html#sec-string.fromcharcode
pub(crate) fn from_char_code(
_: &JsValue,
args: &[JsValue],
context: &mut Context,
) -> JsResult<JsValue> {
// 1. Let length be the number of elements in codeUnits.
// 2. Let elements be a new empty List.
let mut elements = Vec::new();
// 3. For each element next of codeUnits, do
for next in args {
// 3a. Let nextCU be ℝ(? ToUint16(next)).
// 3b. Append nextCU to the end of elements.
elements.push(next.to_u32(context)? as u16);
}
Comment on lines +258 to +264
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Just noting that, when #1552 gets merged, this should be simplified further to:

args.iter()
    .map(|val| val.to_u16(context))
    .collect::<JsResult<Vec<_>>>()?;


// 4. Return the String value whose code units are the elements in the List elements.
// If codeUnits is empty, the empty String is returned.

let s = std::string::String::from_utf16_lossy(elements.as_slice());
Ok(JsValue::String(JsString::new(s)))
}

/// Get the string value to a primitive string
#[allow(clippy::wrong_self_convention)]
#[inline]
Expand Down