Javascript QUEST!

function Person(name, age, job){ this.name = name; this.age = age; this.job = job; this.friends = [“Shelby”, “Court”]; } Person.prototype = { constructor: Person, sayName : function () { alert(this.name); } }; var person1 = new Person(“Nicholas”, 29, “Software Engineer”); var person2 = new Person(“Greg”, 27, “Doctor”);

function forEach(array, action) { for (var i = 0; i < array.length; i++) action(array[i]); } function reduce(combine, base, array) { forEach(array, function (element) { base = combine(base, element); }); return base; } function countZeroes(array) { function counter(total, element) { return total + (element === 0 ? 1 : 0); } return reduce(counter, 0, array); }

function reduce(combine, base, array) { forEach(array, function (element) { base = combine(base, element); }); return base; } -> function reduce(counter, 0, array) { forEach(array, function (element) { base = counter(base, element); }); return base; } -> function reduce( function counter(total, element) { return total + (element === 0 ? 1 : 0); }, 0, array) { forEach(array, function (element) { base = counter(base, element) { base + (element === 0 ? 1 : 0); } }); return base; } -> function reduce( function counter(total, element) { return total + (element === 0 ? 1 : 0); }, 0, array) { for (var i = 0; i < array.length; i++) base = base + (array[i] === 0 ? 1 : 0); return base; }

function counter(total, element) {

total is the accumulator. element is the iterator.

function reduce(combine, base, array) {

function reduce(combine, base, array) { forEach(array, function (element) { base = combine(base, element); }); return base; } function add(a, b) { return a + b; } function sum(numbers) { return reduce(add, 0, numbers); }

function forEach(array, action) { for (var i = 0; i < array.length; i++) action(array[i]); }

function add(a, b) { return a + b; } function sum(numbers) { return reduce(add, 0, numbers); } show(sum([1,2,3,4,5]));

sum([1,2,3,4,5]); -> reduce(add,0,[1,2,3,4,5]); -> reduce( function add(a, b) { return a + b; }, 0, [1,2,3,4,5]); -> reduce(combine, base, array) -> function reduce(add, 0, [1,2,3,4,5]) { forEach([1,2,3,4,5], function (element) { base = add(0, element); }); return base; } -> function reduce(add, 0, [1,2,3,4,5]) { for (var i = 0; i < [1,2,3,4,5].length; i++) function (array[i]) {base = add(0, array[i]);} return base; }

function add(a, b) { return a + b; } function reduce(combine, base, array) { for (var i = 0; i < array.length; i++) { base = add(base, array[i]); show(base); } return base; } reduce(add, 0, [1,2,3,4,5]); 1 3 6 10 15

Expression:

"A piece of code that produces a value is called an expression. Every value that is written directly (such as 22 or "psychoanalysis") is an expression. An expression between parentheses is also an expression. And a binary operator applied to two expressions, or a unary operator applied to one, is also an expression."

Statement:

"There exists a unit that is bigger than an expression. It is called a statement. A program is built as a list of statements. Most statements end with a semicolon (;). The simplest kind of statement is an expression with a semicolon after it. This is a program:"

Write a function range that takes one argument, a positive number, and returns an array containing all numbers from 0 up to and including the given number.

An empty array can be created by simply typing []. Also remember that adding properties to an object, and thus also to an array, can be done by assigning them a value with the = operator. The length property is automatically updated when elements are added.

My solution:

function range(var num) { var array = []; for (var i=0; i < num; ++i) { array[i] = i; } return array; }

Book solutions:

function range(upto) { var result = []; for (var i = 0; i <= upto; i++) result[i] = i; return result; } show(range(4));

Summary:

The solution for the cat problem talks about a 'set' of names. A set is a collection of values in which no value may occur more than once. If names are strings, can you think of a way to use an object to represent a set of names? Show how a name can be added to this set, how one can be removed, and how you can check whether a name occurs in it. My pseudo code:

var catNames = {}; foreach (emails as email) { if (email.catname in catNames) continue; else catNames[catname] = true; } // remove is just a delete

Book Solution:

“we write a program that gives us a list of cats that are still alive after the last e-mail.”

Start with a set of cat names that has only “Spot” in it.

Go over every e-mail in our archive, in chronological order.

Look for paragraphs that start with “born” or “died”.

Add the names from paragraphs that start with “born” to our set of names.

Remove the names from paragraphs that start with “died” from our set.

Pseudo Code

foreach (emails as email) { // #2 if (email.regex('^Spot')) { // #1 array.push(email); if (email.regex('born|died')) { #3 born_array.push(blah) #4 died_array.push(blah) #5 } } }

“Where taking the names from a paragraph goes like this:”

Find the colon in the paragraph.

Take the part after this colon.

Split this part into separate names by looking for commas.

Pseudo Code

function greaterThan(gtNum) { return function(testNum) { if (testNum > gtNum) { return true; } else { return false; } } } var gtTest = greaterThan(5); print(gtTest(8)); var gtTest = greaterThan(5); print(gtTest(1));

Output: true false Book solution:

http://eloquentjavascript.net/chapter3

function findSequence(goal) { function find(start, history) { if (start == goal) return history; else if (start > goal) return null; else return find(start + 5, "(" + history + " + 5)") || find(start * 3, "(" + history + " * 3)"); } return find(1, "1"); } print(findSequence(24));