编程语言中『一等公民』是什么公民？

在 JavaScript 中总是见到一等公民字样，一直很纳闷，什么是一等公民？？？

用必应词典翻译一下，英文叫first-class citizen，再维基百科一下

In programming language design, a first-class citizen (also type, object, entity, or value) in a given programming language is an entity which supports all the operations generally available to other entities. These operations typically include being passed as an argument, returned from a function, and assigned to a variable.

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