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annotated.js

function(
   a, // {Number}: random string length
   b, //         : internal variable: result
   c  //         : internal variable: char code
){
   for (
         b = ''; // result
         a--;    // random string length (arguments[0])
       )
         b += String.fromCharCode((                                  // http://www.w3schools.com/jsref/jsref_fromcharcode.asp
                                  ( c = 0|Math.random() * 52 )       // random value = random * [a-zA-Z]
                                      < 26 ? 65 : 71         ) + c   //              < 26 ? [A-Z] : [a-z]) + random value
                                 );
   return b     // result
}

index.js

export function(a,b,c){for(b='';a--;)b+=String.fromCharCode(((c=0|Math.random()*52)<26?65:71)+c);return b}

PACKAGE.json

{
  "name": "getRandomString",
  "description": "Generate random alpha [a-zA-Z] string.",
  "keywords": [ "random", "string" ],
  "version": "0.1.0"
}