Javascript (一)：Functions As First-Class Things

The term “first-class” means that something is just a value. A first-class function is one that can go anywhere that any other value can go—there are few to no restrictions. A number in JavaScript is surely a first-class thing, and therefore a first-class function has a similar nature.

术语“first-class”仅表示一个数值，基础类Function可以出现“数值”能出现的任何地方（几乎没有限制）。number确实基础类在javascript中，因此基本类Function有相似的特性：

• a number can be stored in a variable and so can a function

  var fortytwo = function() { return 42 };

• a number can be stored in an object field and so can a function:

  var fortytwos = [42, function() { return 42 }];
  

• a number can be stored in an object field and so can a function:

  var fortytwos = {number: 42, fun: function() { return 42 }};

• a number can be created as needed and so can a function:

  42 + (function() { return 42 })();
  //=> 84

• a number can be passed to a function and so can a function:

  function weirdAdd(n, f) { return n + f() };

weirdAdd(42, function() { return 42 }); //=> 84

• a number can be returned from a function and so can a function:

  return 42;
  return function() { return 42 };