chapter: Arrays
  ==================
  var empty = [];
  var numbers = [
      'zero', 'one', 'two', 'three', 'four',
      'five', 'six', 'seven', 'eight', 'nine'
  ];
  
  empty[1]          // undefined
  numbers[1]        // 'one'
  
  empty.length      // 0
  numbers.length    // 10
      
      
  ====================================
  var numbers_object = {
      '0': 'zero',  '1': 'one',   '2': 'two',
      '3': 'three', '4': 'four',  '5': 'five',
      '6': 'six',   '7': 'seven', '8': 'eight',
      '9': 'nine'
  };
      
      
  ====================================
  var misc = [
      'string', 98.6, true, false, null, undefined,
      ['nested', 'array'], {object: true}, NaN,
      Infinity
  ];
  misc.length    // 10
      
      
  ====================================
  var myArray = [];
  myArray.length             // 0
  
  myArray[1000000] = true;
  myArray.length             // 1000001
  // myArray contains one property.
      
      
  ====================================
  numbers.length = 3;
  // numbers is ['zero', 'one', 'two']
      
      
  ====================================
  numbers[numbers.length] = 'shi';
  // numbers is ['zero', 'one', 'two', 'shi']
      
      
  ====================================
  numbers.push('go');
  // numbers is ['zero', 'one', 'two', 'shi', 'go']
      
      
  ====================================
  delete numbers[2];
  // numbers is ['zero', 'one', undefined, 'shi', 'go']
      
      
  ====================================
  numbers.splice(2, 1);
  // numbers is ['zero', 'one', 'shi', 'go']
      
      
  ====================================
  var i;
  for (i = 0; i < myArray.length; i += 1) {
      document.writeln(myArray[i]);
  }
      
      
  ====================================
  var is_array = function (value) {
      return value && typeof value === 'object' && value.constructor === Array;
  };
      
      
  ====================================
  var is_array = function (value) {
      return Object.prototype.toString.apply(value) === '[object 
  Array]';
  };
      
      
  ====================================
  Array.method('reduce', function (f, value) {
      var i;
      for (i = 0; i < this.length; i += 1) {
          value = f(this[i], value);
      }
      return value;
  });
      
      
  ====================================
  // Create an array of numbers.
  
  var data = [4, 8, 15, 16, 23, 42];
  
  // Define two simple functions. One will add two
  // numbers. The other will multiply two numbers.
  
  var add = function (a, b) {
      return a + b;
  };
  
  var mult = function (a, b) {
      return a * b;
  };
  
  // Invoke the data's reduce method, passing in the
  // add function.
  
  var sum = data.reduce(add, 0);    // sum is 108
  
  // Invoke the reduce method again, this time passing
  // in the multiply function.
  
  var product = data.reduce(mult, 1);
      // product is 7418880
      
      
  ====================================
  // Give the data array a total function.
  
  data.total = function (  ) {
      return this.reduce(add, 0);
  };
  
  total = data.total(  );    // total is 108
      
      
  ====================================
  Array.dim = function (dimension, initial) {
      var a = [], i;
      for (i = 0; i < dimension; i += 1) {
          a[i] = initial;
      }
      return a;
  };
  
  // Make an array containing 10 zeros.
  
  var myArray = Array.dim(10, 0);
      
      
  ====================================
  var matrix = [
      [0, 1, 2],
      [3, 4, 5],
      [6, 7, 8]
  ];
  matrix[2][1]    // 7
      
      
  ====================================
  for (i = 0; i < n; i += 1) {
      my_array[i] = [];
  }
  
  // Note: Array.dim(n, []) will not work here.
  // Each element would get a reference to the same
  // array, which would be very bad.
      
      
  ====================================
  Array.matrix = function (m, n, initial) {
      var a, i, j, mat = [];
      for (i = 0; i < m; i += 1) {
          a = [];
          for (j = 0; j < n; j += 1) {
              a[j] = initial;
          }
          mat[i] = a;
      }
      return mat;
  };
  
  // Make a 4 * 4 matrix filled with zeros.
  
  var myMatrix = Array.matrix(4, 4, 0);
  
  document.writeln(myMatrix[3][3]);    // 0
  
  // Method to make an identity matrix.
  
  Array.identity = function (n) {
      var i, mat = Array.matrix(n, n, 0);
      for (i = 0; i < n; i += 1) {
          mat[i][i] = 1;
      }
      return mat;
  };
  
  myMatrix = Array.identity(4);
  
  document.writeln(myMatrix[3][3]);    // 1
      
      
  ==================