It's quite simple: speed. Javascript engines predating V8 tended to be on the slow side, which discouraged in-browser scripts from being complex or large. As a

It's quite simple: speed. Javascript engines predating V8 tended to be on the slow side, which discouraged in-browser scripts from being complex or large. As a result, nobody really cared about the JS object model or the flexibility of the language or pretty much anything other than showing popups. With a fast JS engine and node's async network stack (also fast), it suddenly became a "real" language.