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