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Built-ins

Function

Function

call(thisArg, param...)

It allows your objects to borrow methods from other objects and invoke them as their own.

var greets = function (breed, birth) {
  return "Hi I'm " + this.firstName + " " + breed +
         ", I was born in " + birth + ".";
}

var mickey = {
  firstName: 'Mickey'
};

var donald = {
  firstName: 'Donald'
};

greets.call(mickey, 'Mouse', 1928);
//"Hi I'm Mickey Mouse, I was born in 1928."

greets.call(donald, 'Duck', 1934);
//"Hi I'm Donald Duck, I was born in 1934."

Function

apply(thisArg, arrayArg)

It has the same behaviour of call but different signature.

var greets = function (breed, birth) {
  return "Hi I'm " + this.firstName + " " + breed +
         ", I was born in " + birth + ".";
}

var mickey = {
  firstName: 'Mickey'
};

var donald = {
  firstName: 'Donald'
};

greets.apply(mickey, ['Mouse', 1928]);
//"Hi I'm Mickey Mouse, I was born in 1928."

greets.call(donald, ['Duck', 1934]);
//"Hi I'm Donald Duck, I was born in 1934."

Function

thisArg parameter

if null is passed defaults to the global object

var greets = function (breed, birth) {
  return "Hi I'm " + this.firstName + " " + breed +
         ", I was born in " + birth + ".";
}

greets.apply(null, ['Mouse', 1928]);
//"Hi I'm undefined Mouse, I was born in 1928."

var firstName = 'Goofy';
greets.apply(null, ['Goof', 1932]);
//"Hi I'm Goofy Goof, I was born in 1932."

Array

Array

Definition

var a = ['one', 'two', 'three'];
var empty = [];
var plain = [1+2,'four'];
var matrix = [[1,2,3], [4,5,6], [7,8,9]];
var sparseArray = [1,,,,5];

Arrays are objects, but of a special type because:

  • the names of their properties are automatically assigned using numbers
  • they have a length property which contains the number of elements in the array
var a = ['one', 'two', 'three'];
a.length; //3
typeof a; //"object"

Array

Access

Arrays can be accessed through square bracket notation.

var a = ['one', 'two', 'three'];
a[1]; //"two"
a['1']; //"two"
a[1] = 2
a[1]; //2
var matrix = [[1,2,3], [4,5,6], [7,8,9]];
matrix[0][1]; //2

Array

Methods overview

push(item...)
pop()
shift()
unshift(item...)
reverse()
sort(comparefn)
join(separator)
concat(item...)
slice(start, end)
splice(start, deleteCount, item...)
indexOf(item, startPos)
lastIndexOf(item, startPos)
every(function(item, index, array) {...}, thisArg)
some(function(item, index, array) {...}, thisArg)
filter(function(item, index, array) {...}, thisArg)
forEach(function(item, index, array) {...}, thisArg)
map(function(item, index, array) {...}, thisArg)
reduce(function(prev, cur, index, array) {...}, initVal)
reduceRight(function(prev, cur, index, array) {...}, initVal)

Array

push(item...)

It accepts any number of item to push in the array. It returns the array's new length.

var colors = [];   // create an array
var count = colors.push('red', 'green'); // push any number of items
count;  // 2
colors; // ["red", "green"]

count = colors.push('black');   // push another item on
count;  // 3
colors; // ["red", "green", "black"]

Array

pop()

It acceps no parameter. It returns and removes the last element in the array. If the array is empty, return undefined.

var colors = new Array('red', 'green', 'black');

var item = colors.pop(); // get the last item
item; // "black"
colors.length; // 2
colors; // ["red", "green"]

Array

sort(comparefn)

The default comparing function is the lexicographical order.

var values = [0, 1, 5, 10, 15];
values.sort();
values;   // 0,1,10,15,5
var compare = function (value1, value2) {
 return value1 - value2;
};

var values = [0, 1, 5, 10, 15];
values.sort(compare);
values;   // 0,1,5,10,15

Array

Iterative methods: every, filter, forEach, map, some

Each of the iterative methods accepts two arguments:

  • a function to run on each item
  • an optional scope object in which to run the function (affecting the value of this)

The function passed into one of these methods will receive three arguments:

  1. the array item value
  2. the position of the item in the array
  3. the array object itself

Array

every(iterator, thisArg)

Runs the given function on every item in the array
and returns true if the function returns true for every item.

var numbers = [1,2,3,4,5,4,3,2,1];

var everyResult = numbers.every(function(item, index, array) {
 return (item > 2);
});

everyResult;   //false
var numbers = [3,5,3,4,5,4,3,8,9];

var everyResult = numbers.every(function(item) {
 return (item > 2);
});

everyResult;   //true

Array

some(iterator, thisArg)

Runs the given function on every item in the array and returns true if the function returns true for at least one item.

var numbers = [1,2,3,4,5,4,3,2,1];

var someResult = numbers.some(function(item, index, array) {
 return (item > 2);
});

someResult;   //true
var numbers = [1,2,3,4,5,4,3,2,1];

var someResult = numbers.some(function(item, index, array) {
 return (item > 5);
});

someResult;   //false

Array

filter(iterator, thisArg)

Runs the given function on every item in the array
and returns an array of all items for which the function returns true.

var numbers = [1,2,3,4,5,4,3,2,1];

var filterResult = numbers.filter(function(item, index, array){
 return (item > 2);
});

filterResult;   //[3,4,5,4,3]

Array

forEach(iterator, thisArg)

Runs the given function on every item in the array.
This method has no return value.

var numbers = [1,2,3,4,5,4,3,2,1];

numbers.forEach(function(item, index, array){
   //do something here
});

Array

map(iterator, thisArg)

Runs the given function on every item in the array
and returns the result of each function call in an array.

var numbers = [1,2,3,4,5,4,3,2,1];

var mapResult = numbers.map(function(item, index, array){
   return item * 2;
});

mapResult;   // [2,4,6,8,10,8,6,4,2]

Array

Reduction methods: reduce, reduceRight

Both methods accept two arguments:

  • a function to call on each item
  • an optional initial value upon which the reduction is based

The passed function accepts four arguments:

  1. the previous value
  2. the current value
  3. the item's index
  4. the array object

Any value returned from the function is automatically passed in as the first argument for the next item.

Array

reduce(iterator, initVal)

Perform reduction in left-to-right order.

var values = [1,2,3,4,5];

var sum = values.reduce(function(prev, cur, index, array){
 return prev + cur;
});

sum; // 15

Array

reduceRight(iterator, initVal)

Perform reduction in right-to-left order.

var values = [1,2,3,4,5,15];

var diff = values.reduceRight(function(prev, cur, index, array){
 return prev - cur;
});

diff; // 0

The Math object

The Math object

Properties overview

Math.E        // the value of e, the base of the natural logarithms
Math.LN10     // the natural logarithm of 10
Math.LN2      // the natural logarithm of 2
Math.LOG2E    // the base 2 logarithm of e
Math.LOG10E   // the base 10 logarithm of e
Math.PI       // the value of π
Math.SQRT1_2  // the square root of 1⁄2
Math.SQRT2    // the square root of 2

The Math object

Methods overview

Math.min(n0,n1,...)  // Returns the minimum value
Math.max(n0,n1,...)  // Returns the maximum value
Math.ceil(num)       // Rounds number up to the nearest integer value
Math.floor(num)      // Rounds number down to the nearest integer value
Math.round(num)      // Rounds number
Math.random()        // Returns a random number in [0,1)
Math.exp(num)        // Returns Math.E raised to the power of num
Math.log(num)        // Returns the natural logarithm of num
Math.pow(num, power) // Returns num raised to the power of power
Math.sqrt(num)       // Returns the square root of num
Math.acos(x)         // Returns the arc cosine of x
Math.asin(x)         // Returns the arc sine of x
Math.atan(x)         // Returns the arc tangent of x
Math.atan2(y, x)     // Returns the arc tangent of y/x
Math.cos(x)          // Returns the cosine of x
Math.sin(x)          // Returns the sine of x
Math.tan(x)          // Returns the tangent of x

RegExp

RegExp

Regex literals

var expression = /pattern/flags;

Flags can be:

  • g — global mode, meaning the pattern will be applied to all of the string instead of stopping after the first match is found
  • i — case-insensitive mode, meaning the case of the pattern and the string are ignored when determining matches
  • m — multiline mode, meaning the pattern will continue looking for matches after reaching the end of one line of text

RegExp

Methods overview

exec(str)
test(str)

String

String

Methods overview

charAt(pos)
charCodeAt(pos)
concat(str...)
indexOf(searchString, position)
lastIndexOf(searchString, position)
match(regexp)
search(regexp)
slice(start, end)
split(separator, limit)
toLowerCase()
toUpperCase()

Date

Date

Definition

The Date type stores dates as the number of milliseconds that have passed since midnight on January 1, 1970 UTC (Universal Time Code)

var now = new Date();
now.toDateString(); //"Thu Mar 08 2012"
now.toString();     //"Thu Mar 08 2012 10:41:02 GMT+0100 (CET)"

Date constructor accept many format

var someDate = new Date("May 25, 2004");
var someDate = new Date("25/5/2004");
var someDate = new Date('Tue May 25 2004 00:00:00 GMT-0700');
var someDate = new Date('2004-05-25T00:00:00');