函数调用由一个任意的主题表达式，后跟要给开口的圆括号，逗号分隔表达式作为参数，以闭口的圆括号结束。
Functions calls consist of an arbitrary subject expression followed by an opening parenthesis (, a comma , separated list of expressions as arguments and a closing parenthesis ).
subject(); // call with no arguments
subject(e1); // call with one argument
subject(e1, e2); // call with two arguments
// call with multiple arguments
subject(e1, ..., eN);