feat(boa): implements `at` method for string
* feat(boa): implements `at` method for string
Closes
* cleanup
* fix len
@@ -134,6 +134,7 @@ impl BuiltIn for String {
.method(Self::replace, "replace", 2)
.method(Self::iterator, (symbol_iterator, "[Symbol.iterator]"), 0)
.method(Self::search, "search", 1)
+ .method(Self::at, "at", 1)
.build();
(Self::NAME, string_object.into(), Self::attribute())
@@ -266,6 +267,41 @@ impl String {
}
}
+ /// `String.prototype.at ( index )`
+ ///
+ /// This String object's at() method returns a String consisting of the single UTF-16 code unit located at the specified position.
+ /// Returns undefined if the given index cannot be found.
+ ///
+ /// More information:
+ /// - [ECMAScript reference][spec]
+ /// - [MDN documentation][mdn]
+ ///
+ /// [spec]: https://tc39.es/proposal-relative-indexing-method/#sec-string.prototype.at
+ /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/at
+ pub(crate) fn at(this: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
+ let this = this.require_object_coercible(context)?;
+ let s = this.to_string(context)?;
+ let len = s.encode_utf16().count();
+ let relative_index = args
+ .get(0)
+ .cloned()
+ .unwrap_or_default()
+ .to_integer(context)?;
+ let k = if relative_index < 0 as f64 {
+ len - (-relative_index as usize)
+ } else {
+ relative_index as usize
+ };
+
+ if let Some(utf16_val) = s.encode_utf16().nth(k) {
+ Ok(Value::from(
+ from_u32(u32::from(utf16_val)).expect("invalid utf-16 character"),
+ ))
+ } else {
+ Ok(Value::undefined())
+ }
+ }
+
/// `String.prototype.codePointAt( index )`
///
/// The `codePointAt()` method returns an integer between `0` to `1114111` (`0x10FFFF`) representing the UTF-16 code unit at the given index.
