The function cc.log() doesn't use printf style formatting --  it only takes one argument.  If you log a message that contains %s or other formatting specifiers, the log message will be incorrect.

For example, the code:

cc.log("Foo %s bar");

Should produce a log message like:

JS: Foo %s bar

But before this PR would produce something like:

JS: Foo  [GARBAGE]  bar

Where [GARBAGE] is garbage from the stack.