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I'm taking a course in JavaScript programming, and the instructor said that a typical JavaScript function always returns a value. Even when we don't provide any explicit return value, the engines return undefined
http://stackoverflow.com/questions/20915450/why-javascript-functions-always-return-a-value
Brendan Eich —— 这个人设计了 javascript 语言。
与之相似的， php 也是95年前后有 landeof设计的