Hi Sundar,

startsWith is part of ECMAScript:


Not widely supported...


On 17/10/2016 06:48, Sundararajan Athijegannathan wrote:

"startsWith" is non-standard extension (actually, it is Java method)

jjs> "hello".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



On 10/17/2016 2:20 AM, Esben Andreasen wrote:

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


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

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