Check the validity of a FedEx tracking number based on their 2011 spec

fedexChecker.js

// Depends on ECMAScript 6 for the `map` and `reduce` functions. They are
// easily replaced with a library like Lodash or Underscore.

var FedExChecker = (function() {
  'use strict';

  var CHECK_WEIGHT_ARRAY, TRACKING_NUMBER_MAX_LENGTH, digitsToArray;

  function FedExChecker() {}

  digitsToArray = function( _num ) {
    return _num.toString().split('').map( function( digit ) {
      return parseInt( digit, 10 );
    });
  };

  CHECK_WEIGHT_ARRAY = [1,3,7];
  TRACKING_NUMBER_MAX_LENGTH = 14


  FedExChecker.prototype.isValid = function( _code ) {
    var codeArray, checkDigit, weightedArray, weightedSum;

    codeArray = digitsToArray( _code )

    if ( codeArray.length < 12 ) {
      throw new Error('tracking code cannot be less than 12 digits');
    }

    // Array-ize the tracking code and grab the last 14 digits
    codeArray = codeArray.slice( TRACKING_NUMBER_MAX_LENGTH * -1 );

    // Remove and store the checkDigit from the tracking code
    checkDigit = codeArray.pop();

    // Reverse codeArray for mapping weight
    codeArray = codeArray.reverse();

    // Calculate the code array with weights
    weightedArray = codeArray.map( function( currentValue, index ) {
      var currentWeight = CHECK_WEIGHT_ARRAY[index % CHECK_WEIGHT_ARRAY.length];
      return currentValue * currentWeight;
    });

    // Sum the weighed numbers array
    weightedSum = weightedArray.reduce( function( previousValue, currentValue ) {
      return previousValue + currentValue;
    });

    return (weightedSum % 11) % 10 === checkDigit;
  };


  return FedExChecker;

})();

usage.js

checker = new FedExChecker();

// Providing a well formed FedEx tracking code
checker.isValid(00790112586297);
// true

// Changing the code by one digit (fat fingered user)
checker.isValid(00790112586287);
// false

// Accepts full FedEx barcode
checker.isValid(147701408120018034000790112586297);
// true

// Rejects codes that are too short
checker.isValid(79011258629);
// Error: tracking code cannot be less than 12 digits