参考答案

声明变量有四种方法：

// 声明类型和值，Declaring type and value in a single statement
var [identifier] : [type-annotation] = value; 

// 只声明类型，Declaring type without value
var [identifier] : [type-annotation]; 

// 只声明值，Declaring its value without type
var [identifier] = value; 

// 声明变量无类型和值，Declaring without value and type
var [identifier];