Accessors are only available when targeting ECMAScript 5 and higher.

问题：

运行tsc classes.ts时报如下错误：

error TS1056: Accessors are only available when targeting ECMAScript 5 and higher.

1	error TS1056: Accessors are only available when targeting ECMAScript 5 and higher.

// 运行   
tsc classes.ts -t es5

1 2	// 运行 tsc classes.ts -t es5