String.replace: Deal with missing arguments

src/lib/builtins/string.rs

@@ -4,7 +4,7 @@ use crate::{
         object::{Object, ObjectKind, PROTOTYPE},
         property::Property,
         regexp::{make_regexp, match_all as regexp_match_all, r#match as regexp_match},
-        value::{from_value, to_value, ResultValue, Value, ValueData},
+        value::{from_value, to_value, undefined, ResultValue, Value, ValueData},
     },
     exec::Interpreter,
 };
@@ -738,8 +738,13 @@ pub fn replace(this: &Value, args: &[Value], ctx: &mut Interpreter) -> ResultVal
     let this_str: &str = &ctx.value_to_rust_string(this);
     // We then do the same thing for the other args
     // TODO: what if there are missing arguments?
-    let pattern_str: &str = &ctx.value_to_rust_string(&args[0]);
-    let replacement_str: &str = &ctx.value_to_rust_string(&args[1]);
+    let pattern = get_argument(args, 0);
+    if undefined() == pattern {
+        return Ok(to_value(this_str));
+    }
+    let replacement = get_argument(args, 1);
+    let pattern_str: &str = &ctx.value_to_rust_string(&pattern);
+    let replacement_str: &str = &ctx.value_to_rust_string(&replacement);
     // The Rust pattern is interpreted as a Regex and replaced in the original string with
     // the replacement by using Regex.replace_all
     let result_str = Regex::new(pattern_str)
@@ -748,6 +753,13 @@ pub fn replace(this: &Value, args: &[Value], ctx: &mut Interpreter) -> ResultVal
     Ok(to_value(result_str.into_owned()))
 }
 
+fn get_argument(args: &[Value], idx: usize) -> Value {
+    match args.get(idx) {
+        Some(arg) => arg.clone(),
+        None => undefined(),
+    }
+}
+
 /// Create a new `String` object
 pub fn create_constructor(global: &Value) -> Value {
     // Create constructor function object
@@ -1070,9 +1082,16 @@ mod tests {
         let init = r#"
         var str = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';
         var result = str.replace('dog', 'monkey');
+        var exceptional1 = str.replace();
+        var exceptional2 = str.replace('dog');
         "#;
 
         forward(&mut engine, init);
         assert_eq!(forward(&mut engine, "result"), "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?");
+        assert_eq!(
+            forward(&mut engine, "exceptional1"),
+            "The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?"
+        );
+        assert_eq!(forward(&mut engine, "exceptional2"), "The quick brown fox jumps over the lazy undefined. If the undefined reacted, was it really lazy?");
     }
 }