Training JS #36: methods of Math---kata author's lover:random()

Description:

Maybe you don't often use random() when you're dealing with Kata, but every qualified Kata can not be missing random(). Because random testcase is the most basic anti cheating measure. A variety of testcases also help authors identify potential problems. If you also want to create a new Kata and become an author, please follow me to learn about random().

The definitions and detailed information:

random()

Let's learn the usage of random() through examples:

random() does not require any parameters, and its return value is a decimal between 0 and 1:

for (var i=0;i<5;i++) console.log(Math.random());
//output:
0.9319351236335933
0.5403203193563968
0.006271821213886142
0.6078395291697234
0.4499389610718936

But we usually want to generate some integers, we can do so:

for (var i=0;i<5;i++) console.log(  ~~(100*Math.random()) );
//output:
19
38
69
85
0

A number multiply with random(), and then use the Math.floor(~~ is a simplified form of math.floor) to get an integer. The range is 0 to number-1.

If we do not want to start from 0, but need a specific range, you can write a function do this:

function rndnum(from,to){
  return ~~((to-from)*Math.random()+from);
}
for (var i=0;i<5;i++) console.log(rndnum(20,30));
//output:
20
23
24
24
22

If we want to generate random characters, we can do this:

for (var i=0;i<5;i++) 
  console.log(String.fromCharCode(~~(127*Math.random())));
//output:
<


#
)

We generated a ASCII character. You tell me second and third characters are not generated successfully? No, they're whitespace. If you only want to generate some lowercase letters, you can do this:

for (var i=0;i<5;i++) 
  console.log(String.fromCharCode(~~(26*Math.random()+97)));
//output:
m
p
a
u
r

What should we do if we want to get a character from some of the characters that do not have a regular character? For example, we want to randomly generate a character from aeiou, we can do this:

var chars="aeiou";
for (var i=0;i<5;i++) 
  console.log(chars[~~(chars.length*Math.random())]);
//output:
u
e
i
o
u

If we want to randomly generate some fixed words, we can use arrays to do:

var names=["John","Tom","Jerry","Minne","Alice","othername..."];
for (var i=0;i<5;i++) 
  console.log(names[~~(names.length*Math.random())]);
//output:
Minne
Alice
Jerry
Minne
othername...

Ok, lesson is over. let's us do some task.

Task

Coding in function rndCode. Your task is to generate a random verification code. In accordance with the following rules:

the code length should be 8;
The 1st and 2nd characters should be two uppercase letters. The range is "ABCDEFGHIJKLM".
The 3rd-6th characters should be four numbers.
the 7th and 8th characters should be two symbols. The range is "~!@#$%^&*".
If Your code runs 100 times, It should generate 100 non duplicate verification codes.

Some valid verification code examples:

AB1234#$ MG6145$@ KJ2249@&
CD5678%^ IG7593~% FH8638@&
EF9012!@ GB7047%$ KD7604^%

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