Python has metaclasses, and they're used extensively in many of the frameworks that were critical for those startups (Django etc.). They're coming to Javascript too, in the form of ES6 proxies, which have been long awaited.
I actually think metaclasses are probably a better solution than prototypes, because they let you write the majority of your code in a class-based style and only incorporate funky abstractions when they're really necessary, which is typically infrequently. My point is that prototypes are strictly more powerful than (non-metaclass) class-based systems, and that this power lets you build powerful abstractions that can dramatically decrease the number of lines of code you need to write for an initial system.
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Python has metaclasses, and they're used extensively in many of the frameworks that were critical for those startups (Django etc.). They're coming to Javascript too, in the form of ES6 proxies, which have been long awaited.
I actually think metaclasses are probably a better solution than prototypes, because they let you write the majority of your code in a class-based style and only incorporate funky abstractions when they're really necessary, which is typically infrequently. My point is that prototypes are strictly more powerful than (non-metaclass) class-based systems, and that this power lets you build powerful abstractions that can dramatically decrease the number of lines of code you need to write for an initial system.