js examples

gistfile1.js

// The classic for-loop
var strings = ['1', '2', '3'],
    numbers = [];

for (var i = 0; i < strings.length; i++) {
    var number = parseInt(strings[i]);
    numbers.push(number);
}

// numbers == [1, 2, 3]

// How can we fix this?
function map(array, fun) {
    var newArray = [];
    for (var i = 0; i < array.length; i++) {
        newArray.push(fun(array[i]));
    }
    return newArray;
}

var strings = ['1', '2', '3'],
    numbers = map(strings, parseInt);
// numbers == [1, 2, 3]

// Filter And Reduce
filter([1, 2, 3, 4], function (x) {
    return x % 2 == 0; 
});
// Returns [2, 4]

reduce([1, 2, 3, 4], function (acc, x) {
    return acc + x;
})
// Returns 10

// Map + Filter
var strings = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10'],
    numbers = map(strings, parseInt),
    even = filter(numbers, function (x) {
        return x % 2 == 0;
    });
even[0];
// Returns 2

// Iterative Fibonacci Sequence
var prev = 0, next = 1, result;
while (true) {
    if (prev > 1000) {
        result = prev;
        break;
    } else {
        var tmp = prev;
        prev = next;
        next = tmp + prev;
    }
}

// ArrayIterator
function StopIteration () {}

function Iterator(array) {
    var i = 0;
    this.next = function () {
        if (i < array.length) {
            return array[i++];
        } else {
            throw new StopIteration();
        }
    }
}

var i = new Iterator([1, 2, 3]);
i.next(); // Returns 1
i.next(); // Returns 2
i.next(); // Returns 3
i.next(); // Uncaught #<StopIteration> 

// Exhaust
function exhaust(iterator) {
    var result = [];
    while (true) {
        try {
            result.push(iterator.next());
        } catch (e if e instanceof StopIteration) {
            return result
        }        
    }
}

// Take
function take(iterator, n) {
    var result = [];
    for (var i = 0; i < n; i++) {
        result.push(iterator.next());
    }
    return result;
}

take(new Iterator([1, 2, 3, 4]), 2);
// returns [1, 2]

// Map
function imap(iterator, fun) {
    var next = function () {
        return fun(iterator.next());
    }
    return { next: next }
}

var strings = new Iterator(['1', '2', '3']);
    integers = imap(strings, parseInt);
take(integers, 3);
// Returns [1, 2, 3]

// Filter
function ifilter(iterator, fun) {
    var next = function () {
        while (true) {
            var value = iterator.next();
            if (fun(value)) {
                return value;
            }
        }
    }
    return { next: next };
}

var strings = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10'],
    stringIter = new Iterator(strings),
    numbers = imap(stringIter, parseInt),
    even = ifilter(numbers, function (x) { 
        return x % 2 == 0; 
    });
even.next();
// Returns 2

// Fibonacci
function Fibonacci() {
    var prev = 0, next = 1;
    this.next = function () {
        var tmp = prev;
        prev = next;
        next = tmp + next;
        return tmp;
    }
}

var pred = function (x) { return x > 1000 };
ifilter(new Fibonacci(), pred).next();
// Returns 1597

// Isplit
function isplit(string, separator) {
    var offset = 0,
        next = function () {
        var index = string.indexOf(separator, offset);
        if (index > -1) {
            var substr = string.slice(offset, index);
            offset = index + separator.length;
            return substr;
        }
        throw new StopIteration();
    }
    return {next: next};
}

{
    name: 'John Doe',
    email: '[email protected]',
    phone: '01632 960704'
}

"{name: 'John Doe', email: '[email protected] ...}"
"{name: 'Jane Doe', email: '[email protected] ...}"

function findPerson(json, email) {
    var tokens = isplit(json, "\n"),
        people = imap(tokens, JSON.parse);
    return ifilter(people, function (x) { 
        return x.email == email;        
    }).next();
}