Bug 26904 – Suppress 'undefined' in JSC program display

• Status: RESOLVED
• Resolution: INVALID
• Component: JavaScriptCore

[Brent Fulgham]

If you play with the JSC program, you can perform various calculations and see results:
> 1 + 2
3
> "hello"
hello

The problem is if you attempt to create a variable binding, which does not return a value.  In this case, the JSC program reports 'undefined', which is a surprising result and might confuse a user into thinking an error has occurred.  For example:

> var add2 = function(arg) { return arg + 2; }
undefined
> add2(15)
17

It seems like it would be better if the transcript looked like the following:
> 1 + 2
3
> var add3 = function(arg) { return arg + 3; }
> add3(15)
18

[Oliver Hunt]

The result printed is the result of the expression.  While it may seem odd that "var x = 5" displays undefined that is specified behaviour.  Not doing so would create even more confusion as eval("var x=5") will correctly display undefined.

There's also a reasonable concern that changing this behaviour would break the mozilla js test suite you hit with run-javascriptcore-tests