tl;dr:
变量住在哪里？
在它被定义的环境中。
它会成为 function3 的属性，还是存储在 function3 的其他地方？
No.
JavaScript 是否会遍历某种闭包链，类似于它遍历原型链的方式？
Yes.
它存储在内存中的其他地方吗？
Yes.
tl;dr 2:
函数保留对其创建所在环境的引用。调用函数时，它会创建一个新环境，其父环境是函数保留引用的环境。
更长的解释：
每当执行一个新函数时词汇环境 http://www.ecma-international.org/ecma-262/6.0/index.html#sec-lexical-environments被建造。环境有两个“场”：环境记录 http://www.ecma-international.org/ecma-262/6.0/index.html#sec-environment-records其中所有变量都被跟踪并且外部词汇环境顾名思义，它指的是“父词汇环境”。
因此，当我们评估您的代码示例时，内存的初始状态（在执行任何操作之前）可能如下所示（简化）：
+-(Global) lexical environment-+ +-Environment Record-+
+-------------+----------------+ +---------+----------+
| Environment | *--------+---> |function1|undefined |
| Record | | +---------+----------+
+-------------+----------------+ |function3|undefined |
| Outer | | +---------+----------+
| lexical | (empty) |
| environment | |
+-------------+----------------+
全局环境没有任何外部环境，因为它位于顶部。function1 and function3是两个尚未初始化的绑定（尚未评估赋值）。
创建函数后（评估function1 = function() { ... }），内存看起来像这样：
+------------------------------------------------------------------------+
| |
v |
+-(Global) lexical environment-+ +-Environment Record-+ +-----Function Object-+---+
+-------------+----------------+ +---------+----------+ +---------------+-----+---+
| Environment | *--------+--->|function1| *-----+---->|[[Environment]]| * |
| Record | | +---------+----------+ +---------------+---------+
+-------------+----------------+ |function3|undefined | | name |function1|
| Outer | | +---------+----------+ +---------------+---------+
| lexical | (empty) |
| environment | |
+-------------+----------------+
Now function1有一个值，一个函数对象。函数对象有多个内部（例如[[Environment]]）和外部（例如name） 特性。顾名思义，内部属性无法从用户代码访问。这[[Environment]]财产非常重要。请注意它是如何引用创建该函数的词法环境的！
下一步正在执行function3 = function1()，即调用function2。正如我在一开始所说的，每当执行一个函数时，就会创建一个新的词法环境。我们看一下刚进入函数后的内存：
+------------------------------------------------------------------------+
| |
v |
+-(Global) lexical environment-+ +-Environment Record-+ +-----Function Object-+---+
+-------------+----------------+ +---------+----------+ +---------------+-----+---+
| Environment | *--------+--->|function1| +---->|[[Environment]]| * |
| Record | | +---------+----------+ +---------------+---------+
+> +-------------+----------------+ |function3|undefined | | name |function1|
| | Outer | | +---------+----------+ +---------------+---------+
| | lexical | (empty) |
| | environment | |
| +-------------+----------------+
|
|
|
| +-----lexical environment------+ +-Environment Record-+
| +-------------+----------------+ +---------+----------+
| | Environment | *--------+--->|variable |undefined |
| | Record | | +---------+----------+
| +-------------+----------------+ |function2|undefined |
| | Outer | | +---------+----------+
| | lexical | * |
| | environment | | |
| +-------------+--------+-------+
| |
+-------------------------+
这看起来与全局环境的结构非常相似！我们有一个词法环境，它有一个带有两个未初始化绑定的环境记录。但现在最大的区别是“外部词汇环境”指向全局词汇环境。这怎么可能？
打电话时function1创建一个新的词法环境，我们将新环境“外部词法环境”字段的值设置为function1's [[Environment]]场地。这是我们的作用域链被建造。
现在，执行后function1，存储器具有以下结构：
+------------------------------------------------------------------------+
| |
v |
+-(Global) lexical environment-+ +-Environment Record-+ +-----Function Object-+---+
+-------------+----------------+ +---------+----------+ +---------------+-----+---+
| Environment | *--------+--->|function1| *-----+---->|[[Environment]]| * |
| Record | | +---------+----------+ +---------------+---------+
+> +-------------+----------------+ |function3| | | | name |function1|
| | Outer | | +---------+---+------+ +---------------+---------+
| | lexical | (empty) | |
| | environment | | |
| +-------------+----------------+ +-------------------------+
| |
| +----------------------------------------------------------------+--------+
| v | |
| +-----lexical environment------+ +-Environment Record-+ v |
| +-------------+----------------+ +---------+----------+ |
| | Environment | *--------+--->|variable | 'foo' | +-----Function Object-+---+
| | Record | | +---------+----------+ +---------------+-----+---+
| +-------------+----------------+ |function2| *-----+---->|[[Environment]]| * |
| | Outer | | +---------+----------+ +---------------+---------+
| | lexical | * | | name |function2|
| | environment | | | +---------------+---------+
| +-------------+--------+-------+
| |
+-------------------------+
类似的喜欢function1, function2具有对通过调用创建的环境的引用function2。此外，function3指的是我们创建的函数，因为我们从function1.
最后一步：调用function3('bar'):
+------------------------------------------------------------------------+
| |
v |
+-(Global) lexical environment-+ +-Environment Record-+ +-----Function Object-+---+
+-------------+----------------+ +---------+----------+ +---------------+-----+---+
| Environment | *--------+--->|function1| *-----+---->|[[Environment]]| * |
| Record | | +---------+----------+ +---------------+---------+
+> +-------------+----------------+ |function3| | | | name |function1|
| | Outer | | +---------+---+------+ +---------------+---------+
| | lexical | (empty) | |
| | environment | | |
| +-------------+----------------+ +-------------------------+
| |
| +----------------------------------------------------------------+--------+
| v | |
| +-----lexical environment------+ +-Environment Record-+ v |
| +-------------+----------------+ +---------+----------+ |
| | Environment | *--------+--->|variable | 'foo' | +-----Function Object-+---+
| | Record | | +---------+----------+ +---------------+-----+---+
|+>+-------------+----------------+ |function2| *-----+---->|[[Environment]]| * |
|| | Outer | | +---------+----------+ +---------------+---------+
|| | lexical | * | | name |function2|
|| | environment | | | +---------------+---------+
|| +-------------+--------+-------+
++------------------------+
|
| +-----lexical environment------+ +-Environment Record-+
| +-------------+----------------+ +---------+----------+
| | Environment | *--------+--->|argument | 'bar' |
| | Record | | +---------+----------+
| +-------------+----------------+
| | Outer | |
| | lexical | * |
| | environment | | |
| +-------------+--------+-------+
+------------------------+
与这里类似，创建了一个新环境，其“外部词法环境”字段指向创建时创建的环境function1被称为。
现在，查找argument很简单，因为它存在于环境自己的记录中。但抬头一看variable，会发生以下情况：由于它不存在于环境自己的记录中，因此它会查看其“外部词汇环境”的记录。它可以做到这一点，因为它有一个对它的引用。
