分别实现数组所有元素相加、相乘、相与——FP 风格

var ops = { 
  "plus": (x,y)=>x+y,
  "mul" : (x,y)=>x*y,
  "and" : (x,y)=>x&y
}

function operation(op, array) {
  return array.slice(1).reduce(ops[op], array[0]);
} 

operation("plus", array);
operation("mul",  array);
operation("and",  array);