JavaScript: The First Parts Part Five

1
JavaScript The First PartsPart Five

• Douglas Crockford
• Yahoo! Inc.

2

• var wordify function ()
• var units
• '', 'one', 'two', 'three', 'four',
  'five', 'six', 'seven',
• 'eight', 'nine', 'ten', 'eleven',
  'twelve', 'thirteen',
• 'fourteen', 'fifteen', 'sixteen',
  'seventeen', 'eighteen',
• 'nineteen'
• var tens
• 'ten', 'twenty', 'thirty', 'forty',
  'fifty', 'sixty', 'seventy',
• 'eighty', 'ninety'
• var illions
• '', 'thousand', 'million', 'billion',
  'trillion', 'quadrillion',
• 'quintillion', 'sextillion',
  'septillion', 'octillion',
• 'nonillion', 'decillion'

3

• var wordify function ()
• // The wordify function converts a positive
  integer into English words.
• // The units array contains the names of the
  digits 0-9 as well as the
• // teens which are somewhat irregular in their
  construction. The other
• // numbers below one hundred are not included
  here because they are
• // regular and easily constructed.
• var units
• '', 'one', 'two', 'three', 'four',
  'five', 'six', 'seven',
• 'eight', 'nine', 'ten', 'eleven',
  'twelve', 'thirteen',
• 'fourteen', 'fifteen', 'sixteen',
  'seventeen', 'eighteen',
• 'nineteen'
• var tens
• 'ten', 'twenty', 'thirty', 'forty',
  'fifty', 'sixty', 'seventy',
• 'eighty', 'ninety'

4

• var wordify function ()
• // The wordify function converts a positive
  integer into English words.
• // The units array contains the names of the
  digits 0-9 as well as the
• // teens which are somewhat irregular in their
  construction. The other
• // numbers below one hundred are not included
  here because they are
• // regular and easily constructed.
• var units
• '', 'one', 'two', 'three', 'four',
  'five', 'six', 'seven',
• 'eight', 'nine', 'ten', 'eleven',
  'twelve', 'thirteen',
• 'fourteen', 'fifteen', 'sixteen',
  'seventeen', 'eighteen',
• 'nineteen'
• var tens
• '', 'ten', 'twenty', 'thirty', 'forty',
  'fifty', 'sixty',
• 'seventy', 'eighty', 'ninety'

5

• var wordify function ()
• // The wordify function converts a positive
  integer into English words.
• // The units array contains the names of the
  digits 0-9 as well as the
• // teens which are somewhat irregular in their
  construction. The other
• // numbers below one hundred are not included
  here because they are
• // regular and easily constructed.
• var units
• '', 'one', 'two', 'three', 'four',
  'five', 'six', 'seven',
• 'eight', 'nine', 'ten', 'eleven',
  'twelve', 'thirteen',
• 'fourteen', 'fifteen', 'sixteen',
  'seventeen', 'eighteen',
• 'nineteen'
• // The tens array contains the names of the tens.
• var tens

6

• // The illions contains the names of the powers
  of thousand. Note
• // the largest safe integer is about 9
  quadrillion, so it may be
• // pointless to pretend to handle numbers up to
  the decillions.
• var illions
• '', 'thousand', 'million', 'billion',
  'trillion', 'quadrillion',
• 'quintillion', 'sextillion',
  'septillion', 'octillion',
• 'nonillion', 'decillion'
• return function (n)
• var result '', i, clump, hundred, ten,
  unit, word, illion
• n Math.floor(n)
• if (!n)
• return 'zero'
• for (i 0 i lt illions.length i 1)

7

• // The illions contains the names of the powers
  of thousand. Note
• // the largest safe integer is about 9
  quadrillion, so it may be
• // pointless to pretend to handle numbers up to
  the decillions.
• var illions
• '', 'thousand', 'million', 'billion',
  'trillion', 'quadrillion',
• 'quintillion', 'sextillion',
  'septillion', 'octillion',
• 'nonillion', 'decillion'
• // Return the actual wordify function. It takes a
  number as its argument.
• return function (n)
• var result '', i, clump, hundred, ten,
  unit, word, illion
• n Math.floor(n)
• if (!n)
• return 'zero'

8

• // The illions contains the names of the powers
  of thousand. Note
• // the largest safe integer is about 9
  quadrillion, so it may be
• // pointless to pretend to handle numbers up to
  the decillions.
• var illions
• '', 'thousand', 'million', 'billion',
  'trillion', 'quadrillion',
• 'quintillion', 'sextillion',
  'septillion', 'octillion',
• 'nonillion', 'decillion'
• // Return the actual wordify function. It takes a
  number as its argument.
• return function (n)
• var result '', // The string containing
  the result
• i, // The loop counter
• clump, // The number
  representing 3 digits
• hundred, // The number in the
  hundreds place
• ten, // The number in the
  tens place
• unit, // The number in the
  units place

9

• // Force n to be an integer.
• n Math.floor(n)
• if (!n)
• return 'zero'
• for (i 0 i lt illions.length i 1)
• clump n 1000
• if (clump)
• hundred Math.floor(n / 100)
• unit clump - (hundred 100)
• illion illionsi
• word unitsunit
• if (typeof word ! 'string')
• ten Math.floor(unit / 10)
• unit unit 10
• word unitsunit
• if (word)

10

• // Force n to be an integer.
• n Math.floor(n)
• // If n is zero, return the string 'zero'.
• if (!n)
• return 'zero'
• for (i 0 i lt illions.length i 1)
• clump n 1000
• if (clump)
• hundred Math.floor(n / 100)
• unit clump - (hundred 100)
• illion illionsi
• word unitsunit
• if (typeof word ! 'string')
• ten Math.floor(unit / 10)

11

• // Force n to be an integer.
• n Math.floor(n)
• // If n is zero, return the string 'zero'.
• if (!n)
• return 'zero'
• // Loop for each of the illions
• for (i 0 i lt illions.length i 1)
• clump n 1000
• if (clump)
• hundred Math.floor(n / 100)
• unit clump - (hundred 100)
• illion illionsi
• word unitsunit

12

• // Loop for each of the illions
• for (i 0 i lt illions.length i 1)
• // Get the bottom clump of 3 digits.
• clump n 1000
• // If the clump is not zero, then the clump will
  contribute words to the
• // result.
• if (clump)
• hundred Math.floor(n / 100)
• unit clump - (hundred 100)
• illion illionsi
• word unitsunit
• if (typeof word ! 'string')
• ten Math.floor(unit / 10)
• unit unit 10

13

• // Loop for each of the illions
• for (i 0 i lt illions.length i 1)
• // Get the bottom clump of 3 digits.
• clump n 1000
• // If the clump is not zero, then the clump will
  contribute words to the
• // result.
• if (clump)
• // Get the most significant of the three digits
  in the clump.
• hundred Math.floor(clump /
  100)
• unit clump - (hundred 100)
• illion illionsi
• word unitsunit

14

• // Loop for each of the illions
• for (i 0 i lt illions.length i 1)
• // Get the bottom clump of 3 digits.
• clump n 1000
• // If the clump is not zero, then the clump will
  contribute words to the
• // result.
• if (clump)
• // Get the most significant of the three digits
  in the clump.
• hundred Math.floor(clump /
  100)
• // Get the remaining digits in the clump.

15

• // Get the remaining digits in the clump.
• unit clump - (hundred 100)
• // Get the name of the power of thousand.
• illion illionsi
• // Get the name of the unit part and put it into
  word.
• // If there isn't a name, then the value of word
  will be undefined.
• word unitsunit
• if (typeof word ! 'string')
• ten Math.floor(unit / 10)
• unit unit 10
• word unitsunit
• if (word)
• word ' ' word

16

• // Get the name of the unit part and put it into
  word.
• // If there isn't a name, then the value of word
  will be undefined.
• word unitsunit
• // If word does not contain a string, then
  extract the tens digit and
• // the units digit.
• if (typeof word ! 'string')
• ten Math.floor(unit / 10)
• unit unit 10
• word unitsunit
• // If the unit is not zero, add its name to the
  word.
• if (word)
• word ' ' word

17

• // If the hundred digit is not zero, then add the
  hundred's text to the
• // word, including the word 'hundred' and spaces
  where needed.
• if (hundred)
• if (word)
• word ' ' word
• word unitshundred '
  hundred' word
• if (result)
• result ' ' result
• result word result
• n Math.floor(n / 1000)
• if (n 0)
• break

18

• // If the result is not an empty string, then add
  a space to it to
• // separate the previous result from the
  contribution of this clump.
• if (result)
• result ' ' result
• // Add the result of this clump to the result.
• result word result
• n Math.floor(n / 1000)
• if (n 0)
• break
• return result

19

• // If the result is not an empty string, then add
  a space to it to
• // separate the previous result from the
  contribution of this clump.
• if (result)
• result ' ' result
• // If the power of thousands has a name, include
  it.
• if (illion)
• word ' ' illion
• // Add the result of this clump to the result.
• result word result
• n Math.floor(n / 1000)
• if (n 0)

20

• // Divide n by a thousand to remove the current
  clump. That sets the
• // loop up to handle the next clump.
• n Math.floor(n / 1000)
• // If n went to zero, then there is no need to
  test the remaining powers of
• // thousand. We can finish early.
• if (n 0)
• break
• // That completes the loop.
• // Return the result. (This is a useless
  comment.)
• return result

21

• // Divide n by a thousand to remove the current
  clump. That sets the
• // loop up to handle the next clump.
• n Math.floor(n / 1000)
• // If n went to zero, then there is no need to
  test the remaining powers of
• // thousand. We can finish early.
• if (n 0)
• break
• // That completes the loop.
• return result
• // Execute the outer function.

22
Wrapping a loop in a function

• var reduce function (array, func)
• var i, length array.length, result
  array0
• for (i 1 i lt length i 1)
• result func(result, arrayi)
• return result
• total reduce(1,2,3,4,5, function (a, b)
• return a b
• )
• product reduce(1,2,3,4,5, function (a, b)
  
• return a b
• )

23
Recursive Function

• var reduce function (array, func)
• var i 0, length array.length, step
• step function (result)
• i 1
• if (i lt length)
• return step(func(result,
  arrayi))
• else
• return result
• return step(array0)

24
Average

• var average function (array)
• var total reduce(array, function (a, b)
  
• return a b
• )
• return total / array.length
• mean average(1,2,3,4,5)

25
Map

• var map function (array, func)
• var i, length array.length, result
  
• for (i 0 i lt length i 1)
• resulti func(arrayi)
• return result
• doubled map(1,2,3,4,5, function (a)
• return a 2
• )

26
A little database

• var database
• aka "burds.b", id "kladenheim", gender
  "f", lucky 3
• ,
• aka "corevette", id "dewqazxc86474",
  gender "m", lucky 42
• ,
• aka "hopdude", id "sergemerov", gender
  "m", lucky 8
• ,
• aka "kaeru", id "leslie.hamachi", gender
  "f", lucky 4
• ,
• aka "lmperry", id "lmperry11", gender "f",
  lucky 7
• ,
• aka "minchew", id "minchew01", gender "f",
  lucky 14
• ,
• aka "moongodess", id "catherinex06",
  gender "f", lucky 20
• ,
• aka "necroskiss", id "pigganon", gender
  "f", lucky 12

27
Select

• var ids map(database, function (record)
• return record.id
• )
• var select function (database, name)
• return map(database, function (record)
• return recordname
• )
• var ids select(database, 'id')

28
Filter

• var filter function (array, func)
• var i, length array.length, result
  
• for (i 0 i lt length i 1)
• if (func(arrayi))
• result.push(arrayi)
• return result
• var girls filter(database, function
  (record)
• return record.gender 'f'
• )

29
Where

• var boys filter(database, function (record)
  
• return record.gender 'm'
• )
• var where function (array, name, value)
• return filter(array, function (record)
• return recordname value
• )
• boys where(database, 'gender', 'm')

30
Average girls' lucky number

• average_girls_lucky_number
• average(select(where(
• database, 'gender', 'f'), 'lucky'))

31
Assignments

• Read Chapter 2.
• Due next week Adapt wordify to another language.
• The program should be fully commented.
• We will read all of the programs in class.