Hi,
"startsWith" is non-standard extension (actually, it is Java method)
jjs> "hello".startsWith
[jdk.internal.dynalink.beans.OverloadedDynamicMethod
java.lang.String.startsWith]
"startsWith" is not an ECMAScript standard specified property of
String.prototype. In Nashorn, you can call methods of java.lang.String
on JS strings. "split" is an ECMAScript standard specified property of
String.prototype and hence you find it as "function" valued property of
String.prototype.
HTH,
-Sundar
On 10/17/2016 2:20 AM, Esben Andreasen wrote:
> Hi
>
> I am not sure if this is a bug or feature of the Nashorn engine. But
> it looks like some String-prototype methods are missing, yet the
> methods are somehow present when used in the right way.
>
> Minimal example: calling `startsWith` by using `call`:
>
> ```
> 1 $ jjs -v
> 2 jjs> String.prototype.startsWith.call('abc', 'ab')
> 3 <shell>:1 TypeError: Cannot read property "call" from undefined
> ```
>
> Expected behavior:
>
> Not a type error, for multiple reasons:
>
> 1. Other JavaScript engines do not throw a type error.
> 2. The equivalent code `"abc".startsWith("ab")` does not throw a type error.
>
>
> Further investigation:
>
> ```
> 1 $ jjs -v
> 2 nashorn 1.8.0_101
> 3 jjs> "abc".startsWith('ab')
> 4 true
> 5 jjs> "abc".startsWith
> 6 [jdk.internal.dynalink.beans.OverloadedDynamicMethod
> boolean java.lang.String.startsWith(String,int)
> boolean java.lang.String.startsWith(String)
> ]
> 7 jjs> "abc".startsWith.call("abc", "ab")
> 8 <shell>:1 TypeError: "abc".startsWith.call is not a function
> 9 jjs> typeof String.prototype.startsWith
> 10 undefined
> 11 jjs> String.prototype.split.call("abc", "b")
> 12 a,c
> ```
>
> Interpretation:
>
> It looks like `startsWith` is not present on the String-prototype, yet
> it is present on the String-primitives. Other String-prototype methods
> (`split`) are however present.
>
> Further notes:
>
> This also applies to `String.prototype.endsWith`.
>
>
> Related bug/feature: primitive values are not wrapped properly:
>
> ```
> 1 $ jjs -v
> 2 jjs> typeof Object("abc").startsWith
> 3 undefined
> ```
