https://codeday.me/bug/20170521/16608.html
是的，JSON数组中的元素的顺序被保留。从RFC 7159 -The JavaScript Object Notation (JSON) Data Interchange Format
(强调我)：
An object is an unordered collection of zero or more name/value
pairs, where a name is a string and a value is a string, number,
boolean, null, object, or array.
An array is an ordered sequence of zero or more values.
The terms “object” and “array” come from the conventions of
JavaScript.
