参数类型注解

声明函数时，可以在每个参数后面加上类型注解，声明函数接受哪些类型的参数。 参数类型注释在参数名称之后：

When you declare a function, you can add type annotations after each parameter to declare what types of parameters the function accepts. Parameter type annotations go after the parameter name:

// Parameter type annotation
function greet(name: string) {
  //                 ^^^^^^^^
  console.log("Hello, " + name.toUpperCase() + "!!");
}

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declare function greet(name: string): void;

// Would be a runtime error if executed!
greet(42);

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