Fix for 0 length new String (#404)

* Fix for 0 length field when constructing a new String.

* String.length uses character count not byte count. Also, corresponding test

* Made tests more succinct per suggestion.

boa/src/builtins/string/mod.rs

@@ -35,13 +35,16 @@ use std::{
 pub fn make_string(this: &mut Value, args: &[Value], _: &mut Interpreter) -> ResultValue {
     // This value is used by console.log and other routines to match Obexpecty"failed to parse argument for String method"pe
     // to its Javascript Identifier (global constructor method name)
+    let s = args
+        .get(0)
+        .expect("failed to get StringData for make_string()")
+        .clone();
+    let length_str = s.to_string().chars().count();
+
+    this.set_field_slice("length", Value::from(length_str as i32));
+
     this.set_kind(ObjectKind::String);
-    this.set_internal_slot(
-        "StringData",
-        args.get(0)
-            .expect("failed to get StringData for make_string()")
-            .clone(),
-    );
+    this.set_internal_slot("StringData", s);
 
     let arg = match args.get(0) {
         Some(v) => v.clone(),

boa/src/builtins/string/tests.rs

@@ -36,6 +36,32 @@ fn check_string_constructor_is_function() {
 //     assert_eq!(d, String::from("4"));
 // }
 
+#[test]
+fn new_string_has_length() {
+    let realm = Realm::create();
+    let mut engine = Executor::new(realm);
+    let init = r#"
+        let a = new String("1234");
+        a
+        "#;
+
+    forward(&mut engine, init);
+    assert_eq!(forward(&mut engine, "a.length"), "4");
+}
+
+#[test]
+fn new_utf8_string_has_length() {
+    let realm = Realm::create();
+    let mut engine = Executor::new(realm);
+    let init = r#"
+        let a = new String("中文");
+        a
+        "#;
+
+    forward(&mut engine, init);
+    assert_eq!(forward(&mut engine, "a.length"), "2");
+}
+
 #[test]
 fn concat() {
     let realm = Realm::create();