/**
 * Request timeout in milliseconds.
 * @type {number}
 */
goog.example.TIMEOUT_IN_MILLISECONDS = 60;

着实没明白什么意思

@tyoe {number} 标记之后,编译器就能主动识别常量?

Note that @const does not necessarily imply CONSTANT_VALUES_CASE. However, CONSTANT_VALUES_CASE does imply @const.

/**
 * Request timeout in milliseconds.
 * @type {number}
 */
goog.example.TIMEOUT_IN_MILLISECONDS = 60;

The number of seconds in a minute never changes. It is a constant value. ALL_CAPS also implies @const, so the constant cannot be overwritten.

The open source compiler will allow the symbol it to be overwritten because the constant is not marked as @const.

/**
 * Map of URL to response string.
 * @const
 */
MyClass.fetchedUrlCache_ = new goog.structs.Map();

In this case, the pointer can never be overwritten, but value is highly mutable and not constant (and thus in camelCase, not ALL_CAPS).