编写一个函数来返回一个数字的阶乘。
一个数字的因子由下式给出:
N! = n *(n-1)*(n-2)* ..... * 1例如:3! = 3 * 2 * 1 = 6 4! = 4 * 3 * 2 * 1 = 24
注意:0! = 1
factorial
是一种功能。
testString: 'assert(typeof factorial === "function", "factorial
is a function.");'
- text: factorial(2)
应该返回一个数字。
testString: 'assert(typeof factorial(2) === "number", "factorial(2)
should return a number.");'
- text: factorial(3)
应该返回6.“)
testString: 'assert.equal(factorial(3),results[0],"factorial(3)
should return 6.");'
- text: factorial(3)
应返回120.“)
testString: 'assert.equal(factorial(5),results[1],"factorial(3)
should return 120.");'
- text: 'factorial(3)
应返回3,628,800。“)'
testString: 'assert.equal(factorial(10),results[2],"factorial(3)
should return 3,628,800.");'
```