Built-ins

IDNameDescriptionTypeModuleStepExplanationExample
1 alert

alert

 JS 1 3

Create a new window containing the message.

The result of alert("Click now") is a box with the string "Click now" which needs to be clicked for you to regain control of your machine.
2 document.write

document write

 JS 1 3

Replaces the content of the page with the input.

The result of document.write("message") is a page with "message" on it.
3 console.log

console log

 JS 1 3

Prints the input to the console.

The result of console(5) is the printing of 5 to the console.
4 var

variable or constant declaration

 JS 2 7

Used to declare a variable or a constant.

Using var cost declares a variable, and var cost = 100; also initializes it.
5 undefined

undefined

 JS 2 7

A built-in value, such as the value of a variable that has not been initialized.

The value of a variable that has not been initialized is undefined.
6 null

null

 JS 2 9

A built-in value.

The type of null is object.
7 typeof

typeof function

 JS 2 9

A function that returns the type of the input.

The value of typeof(5) is "number".
8 Infinity

infinity

 JS 2 10

A special number for infinite values.

The value of 7 / 0 is Infinity.
9 -Infinity

negative infinity

 JS 2 10

A special number for infinite negative values.

The value of -7 / 0 is -Infinity.
10 NaN

not a number

 JS 2 10

A special value to indicate that what has been obtained is not a number.

The value of Infinity / -Infinity is NaN. Paradoxically, the type of NaN is "number".
11 +

addition/concatenation

 JS 2 10

Used to add two numbers or concatenate two strings.

The value of 2 + 3 is 5 and the value of "a" + "b" is "ab".
12 -

subtraction

 JS 2 10

Used to subtract a number from a number.

The value of 5 - 2 is 3.
13 *

multiplication

 JS 2 10

Used to multiply two numbers.

The value of 2 * 3 is 6.
14 /

division

 JS 2 10

Used to divide a number by a number.

The value of 6 / 2 is 3.
15 %

remainder

 JS 2 10

Used to determine the remainder when dividing one number by another.

The value of 6 % 4 is 2.
16 +=

add and update

 JS 2 12

Used to add a value to a variable.

The result of a += b is the same as the result of a = a + b.
17 -=

subtract and update

 JS 2 12

Used to subtract a value from a variable.

The result of a -= b is the same as the result of a = a - b.
18 ++

increment

 JS 2 12

Used to increment a variable.

The result of a++ is the same as the result of a = a + 1.
19 --

decrement

 JS 2 12

Used to decrement a variable.

The result of a-- is the same as the result of a = a - 1.
20 \'

escape character for single quote

 JS 2 13

Used to include a single quotation mark in a string.

An example of a string is "What\'s that?".
21 \"

escape character for double quote

 JS 2 13

Used to include a double quotation mark in a string.

An example of a string is "You are my \"friend\"."
22 \n

escape character for new line

 JS 2 13

Used to indicate where a new line starts in a string.

An example of a string is "One\ntwo"; this appears on two lines.
23 \t

escape character for tab

 JS 2 13

Used to indicate where a tab is placed in a string.

An example of a string is "One\ttwo", with a tab between the two words.
24 \\

escape character for backslash

 JS 2 13

Used to include a backslash in a string.

An example of a string is "This is a backslash: \\".
25 true

Boolean value

 JS 2 14

The Boolean constant true.

The value of true is true.
26 false

Boolean value

 JS 2 14

The Boolean constant false.

The value of false is false.
27 Boolean()

Boolean function

 JS 2 14

Produces the Boolean equivalent of the input.

The value of Boolean("cat") is true.
28 <

less than

 JS 2 15

Produces true when the first input has a value less than the second input.

The value of 3 < 4 is true.
29 <=

less than or equal to

 JS 2 15

Produces true when the first input has a value less than or equal to the second input.

The value of 6 <= 2 is false.
30 >

greater than

 JS 2 15

Produces true when the first input has a value less than the second input.

The value of 3 > 3 is false.
31 >=

greater than or equal to

 JS 2 15

Produces true when the first input has a value greater than or equal to the second input.

The value of 4 >= 4 is true.
32 ==

equal

 JS 2 15

Produces true when the first input has a value equal to the second input, allowing type conversion.

The value of 2 == 2 is true.
33 !=

not equal

 JS 2 15

Produces true when the first input has a value not equal to the second input, allowing type conversion.

The value of 2 != 1 is true.
34 ===

equal (same type)

 JS 2 15

Produces true when the first input has a value equal to the second input, no type conversion allowed.

The value of 2 === 2 is true.
35 !==

not equal (same type)

 JS 2 15

Produces true when the first input has a value not equal to the second input, no type conversion allowed.

The value of 2 !== 3 is true.
36 &&

Boolean and

 JS 2 15

Produces true when both smaller expressions are true.

The value of true && false is false.
37 ||

Boolean or

 JS 2 15

Produces true when at least one smaller expression is true.

The value of false || true is true.
38 !

Boolean not

 JS 2 15

Produces true when the value is False and False when the value is true.

The value of !false is true.
39 Number()

number function

 JS 2 18

Produces the number equivalent (if any) of the input.

The value of Number("5") is 5.
40 String()

string function

 JS 2 18

Produces the string equivalent (if any) of the input.

The value of String(5) is "5".
41 .length

length property

 JS 3 2

A string property with value the number of characters in the string.

The value of "hat".length is 3.
42 .valueOf()

value of method

 JS 3 2

A method of any input, giving its value.

The value of valueOf(3) is 3.
43 .toString()

to string method

 JS 3 2

A method of any input, giving its string equivalent.

The value of 3.toString is "3".
44 .slice(start, stop)

slice method

 JS 3 4

Produces a string with characters positions start through stop - 1.

The value of "hat".slice(1, 2) is "a".

45 .indexOf(sub)

index of method

 JS 3 4

Produces the first position where sub is found, or -1 if it is not present.

The value of "hat".indexOf("a") is 1.
46 .charAt(index)

char at method

 JS 3 4

Produces the character at position index if index is a valid position in the string.

The value of "hat".charAt(2) is "t".

47 .toUpperCase()

to upper case method

 JS 3 4

Produces the string with all lower-case letters replaced by upper-case letters.

The value of "One hat?".toUpperCase is "ONE HAT?".
48 .toLowerCase()

to lower case method

 JS 3 4

Produces the string with all upper-case letters replaced by lower-case letters.

The value of "One hat?".toLowerCase is "one hat?".
49 .replace(old, new)

replace method

 JS 3 4

Produces the string with the first copy of substring old replaced by substring new.

The value of "hat".replace("h","c") is "cat".
50 Math.PI

constant pi

 JS 3 5

The constant pi.

The value of Math.PI is an approximation of pi, 3.141592653589793.
51 Math.floor(n)

math floor

 JS 3 5

Produces the nearest integer below n.

The value of Math.floor(2.5) is 2.
52 Math.ceil(n)

math ceiling

 JS 3 5

Produces the nearest integer above n.

The value of Math.ceil(2.5) is 3.
53 Math.max(a, b, c)

math maximum

 JS 3 5

Produces the maximum of the inputs.

The value of Math.max(1, 2, 3) is 3.
54 Math.min(a, b, c)

math minimum

 JS 3 5

Produces the minimum of the inputs.

The value of Math.min(1, 2, 3) is 1.
55 Math.pow(a, b)

math exponent

 JS 3 5

Produces a to the power b.

The value of Math.pow(2, 3) is 8.
56 Math.sqrt(n)

math square root

 JS 3 5

Produces the square root of n.

The value of Math.sqrt(4) is 2.
57 Math.random()

math random

 JS 3 5

Produces a pseudorandom number in the range [0,1).

The value of Math.random() * 10 is a pseudorandom number in the range from 0 to 9.
58 new Date()

date function

 JS 3 6

Produces a new date object.
59 .getFullYear()

get full year method

 JS 3 6

Produces the full year of a date object.
60 .getMonth()

get month method

 JS 3 6

Produces the month of a date object, numbered from 0 to 11.
61 .getDate()

get date method

 JS 3 6

Produces the date of a date object, with days numbered starting from 1.
62 .getHours()

get hours method

 JS 3 6

Produces the hours of a date object.
63 .getMinutes()

get minutes method

 JS 3 6

Produces the minutes of a date object.
64 .getSeconds()

get seconds method

 JS 3 6

Produces the seconds of a date object.
65 .setMonth()

set month method

 JS 3 6

Sets the month of the data object to the input month.
66 .toDateString()

to date string method

 JS 3 6

Gives a readable format to a date object.
67 canvas.getContext("2d")

get context method

 JS 3 9

Retrieves the context object.
68 lineWidth

line width property

 JS 3 9

A canvas property with value the width of the line in pixels.
69 strokeStyle

stroke style property

 JS 3 9

A canvas property with value a string giving the colour of the line.
70 lineCap

line cap property

 JS 3 9

A canvas property with value a string indicating how the ends of the line can be shaped, such as "butt", "round", and "square".
71 fillStyle

fill style property

 JS 3 9

A canvas property with value a string giving the colour of a closed path.
72 font

font property

 JS 3 9

A canvas property with value a string giving the size and name of a font.
73 .moveTo(x, y)

move to method

 JS 3 10

A canvas method that places the pen at point (x, y).

74 .lineTo(x, y)

line to method

 JS 3 10

A canvas method that forms a line by moving the pen to point (x, y).
75 .stroke()

stroke method

 JS 3 10

A canvas method that makes a line appear using lineWidth and strokeStyle.
76 .beginPath()

begin path method

 JS 3 10

A canvas method that starts a new shape.

77 .closePath()

close path method

 JS 3 10

A canvas method that closes of the shape formed.
78 .fill()

fill method

 JS 3 10

A canvas method that fills what was created.
79 .rect(x, y, w, h)

rectangle method

 JS 3 12

A canvas method that creates a rectangle of width w and height h with the top left corner at (x, y).
80 .arc(x, y, r, s, e)

arc method

 JS 3 12

A canvas method that creates an arc of a circle centred at (x, y) with radius r from starting angle s to ending angle e.
81 .fillText(text, x, y)

fill text method

 JS 3 12

A canvas method that places text at (x, y).
82 documentElement

document element property

 JS 4 2

A DOM property of the document node, meaning the html element.
83 head

head property

 JS 4 2

A DOM property of the document node, meaning the head element.
84 body

body property

 JS 4 2

A DOM property of the document node, meaning the body element.
85 nodeType

node type property

 JS 4 2

A DOM property of any node with value a number indicating the type.
86 nodeName

node name property

 JS 4 2

A DOM property of any node with value a string with tag name in upper case, attribute name, or "#text".
87 nodeValue

node value property

 JS 4 2

A DOM property of any node with value null for an element node, the attribute value for an attribute node and the content for a text node.
88 .getElementById()

get element by ID method

 JS 4 2

A DOM method that produces the element with the ID equal to the input string.
89 parentNode

parent node property

 JS 4 4

A DOM property with value the parent node.
90 firstChild

first child property

 JS 4 4

A DOM property with value the first child node.
91 firstElementChild

first element property

 JS 4 4

A DOM property with value the first child that is an element node.
92 lastChild

last child property

 JS 4 4

A DOM property with value the last child node.
93 lastElementChild

last element child property

 JS 4 4

A DOM property with value the last child that is an element node.
94 nextSibling

next sibling property

 JS 4 4

A DOM property with value the next sibling node.
95 nextElementSibling

next element sibling property

 JS 4 4

A DOM property with value the next sibling that is an element node.
96 previousSibling

previous sibling property

 JS 4 4

A DOM property with value the previous sibling node.
97 previousElementSibling

previous element sibling property

 JS 4 4

A DOM property with value the previous sibling that is an element node.
98 innerHTML

inner HTML property

 JS 4 6

A DOM property with value the entire HTML content of the element.
99 textContent

text content property

 JS 4 6

A DOM property with value the concatenation of the text of all the descendants of the node.
100 style

style property

 JS 4 6

A DOM property with value the style of a node.
101 .getAttribute(attribute)

get attribute method

 JS 4 6

A DOM method that produces the value of a particular attribute.
102 .setAttribute(attribute, value)

set attribute method

 JS 4 8

A DOM method that sets the value of a particular attribute.
103 document.createElement("tagname")

create element method

 JS 4 10

A DOM method that creates an element node with the specified tag name.
104 document.createTextNode("new text")

create text node method

 JS 4 10

A DOM method that creates a text node with the specified text content.
105 .appendChild(item)

append child method

 JS 4 10

A DOM method that adds item as the last child of the object.
106 .insertBefore(item, previousChild)

insert before method

 JS 4 10

A DOM method that inserts item before the child previousChild of the object.
107 .replaceChild(item, oldChild)

replace child method

 JS 4 10

A DOM method that replaces the child oldChild of the object with item.
108 .removeChild(oldChild)

remove child method

 JS 4 13

A DOM method that removes the child oldChild of the object.
109 window.onload

window load

 JS 5 9

The event when the window loads.
110 .addEventListener(event, function)

add event listener method

 JS 5 11

A method that specifies that the function should be executed when the event occurs.
111 if

if

 JS 6 2

Used to introduce the condition and the sequence of steps to execute if the condition is true.
112 else if

else if

 JS 6 2

Used to introduce another condition and the sequence of steps to execute if that condition is true.
113 else

else

 JS 6 2

Used to introduce the sequence of steps to execute if no other branches have been taken.
114 switch

switch

 JS 6 5

Used to specify an expression, the value of which is used to distinguish among cases.
115 case

case

 JS 6 5

Used to specify a possible value of an expression in a switch statement.
116 break

break statement

 JS 6 5

Used to specify a break in a switch statement or an early exit from a loop.
117 while

while loop

 JS 6 7

Used for a while loop.
118 for

for loop

 JS 6 7

Used for a for loop.
119 continue

continue statement

 JS 6 7

Used to specify an exit out of the current iteration in a loop.
120 [item1, item2, item3]

create array

 JS 7 2

Used to create a new array.
121 myArray[i]

array index

 JS 7 2

Used to access the item in the array at index i.

The value of [4, 5][0] is 4.
122 myArray.length

array length

 JS 7 2

Used to specify one greater than the largest index storing an element.

The value of [4, 5].length is 2.
123 .split(string)

split method

 JS 7 2

A string method that consumes a string and produces an array of strings formed by splitting using the input string.

The value of "a-b-c".split("-") is ["a", "b", "c"].
124 .concat(arrayOne, arrayTwo)

concatenation method

 JS 7 6

An array method that returns a new array formed by concatenating arrayOne and arrayTwo to the array; one or more arguments can be used.

The value of [3].concat([4, 5]) is [3, 4, 5].
125 .toString()

to string method

 JS 7 6

An array method that returns a string formed by concatenating all the items, using the string "," between each consecutive pair.

The value of [4, 5].toString() is "4,5".
126 .join(joiner)

join method

 JS 7 6

An array method that returns a string formed by concatenating all the items, using the string joiner between each consecutive pair.

The value of [4, 5].join("-") is "4-5".
127 .indexOf(item)

index of method

 JS 7 6

An array method that returns the index of the leftmost occurrence of the item.

The value of [4, 5, 4].indexOf(4) is 0.
128 .lastIndexOf(item)

last index of method

 JS 7 6

An array method that returns the index of the rightmost occurrence of the item.

The value of [4, 5, 4].lastIndexOf(4) is 2.
129 .slice(start, end)

slice method

 JS 7 6

An array method that returns a new array formed including elements with index start up through end - 1.

The value of [4, 5, 6].slice(1,2) is [5].
130 .slice(start)

slice method (one index)

 JS 7 6

An array method that returns a new array formed including elements with index start up through the end of the original array.

The value of [4, 5, 6].slice(1) is [5, 6].

131 .push(itemOne, itemTwo)

push method

 JS 7 7

An array method that adds the arguments (one or more) to the end of the array and returns the new array length.

Calling [4, 5].push(6) results in the array [4, 5, 6] and the return value 3.
132 .pop()

pop method

 JS 7 7

An array method that removes the last item from the array and returns it.

Calling [4, 5].pop() results in the array [4] and the return value 5.
133 .shift()

shift method

 JS 7 7

An array method that removes the first item from the array and returns it.

Calling [4, 5].shift() results in the array [5] and the return value 4.
134 .unshift(item)

unshift method

 JS 7 7

An array method that adds item to the beginning of the array and returns the array length.

Calling [4].unshift(5) results in the array [5, 4] and the return value 2.
135 .splice(i, num, itemOne, itemTwo)

splice method

 JS 7 8

An array method that splices in the items to add (the third and following arguments) at index i while removing num items, and returns an array of the items removed.

Calling [4, 5, 6, 7, 8].split(1, 2, 9, 10) results in the array [4, 9, 10, 7, 8] and the return value [5, 6].
136 .reverse()

reverse method

 JS 7 8

An array method that reverse the order of the items and returns the modified array.

Calling [4, 5].reverse() results in the array [5, 4] and the return value [5, 4].
137 .sort()

sort method

 JS 7 8

An array method that sorts the items in alphabetical order and returns the modified array.

Calling [8, 6].sort() results in the array [6, 8] and the return value [6, 8].
138 .forms()

forms method

 JS 7 11

A DOM method of the document object that returns all form elements in the body.
139 .images()

images method

 JS 7 11

A DOM method of the document object that returns all images elements in the body.
140 .links()

links method

 JS 7 11

A DOM method of the document object that returns all hyperlink elements in the body.
141 .getElementsByClassName(class)

get elements by class name method

 JS 7 11

A DOM method that returns all elements with the specified class name.
142 .getElementsByTagName(tag)

get elements by tag name method

 JS 7 11

A DOM method that returns all elements with the specified tag name.
143 .getElementsByName(name)

get elements by name method

 JS 7 11

A DOM method of the document object that returns all elements with the specified name.
144 .childNodes()

child nodes method

 JS 7 11

A DOM method that returns all children.
145 .querySelectorAll(selector)

query selector all method

 JS 7 11

A DOM method that returns all elements matching the input selector.
146 objectName = {property: value}

create object

 JS 8 2

Used to create an object.
147 object[property]

extract property

 JS 8 2

Used to extract a property value of an object.
148 delete

delete property

 JS 8 2

Used to delete a property from an object.
149 for (prop in object)

for loop in an object

 JS 8 2

Used to loop over all properties in an object.
150 function Classname()

create class

 JS 8 4

Used to create a class.
151 new ClassName()

create object of a class

 JS 8 4

Used to create an object of a particular class.
152 i

case insensitive modifier

 JS 8 10

Used an a case-insensitive modifier in a regular expression.
153 g

global modifier

 JS 8 10

Used as a global modifier in a regular expression.
154 m

multiline matching modifier

 JS 8 10

Used as a multiline match in a regular expression.
155 .search(exp)

search method

 JS 8 10

A string method that consumes a regular expression and produces the position of the first match.
156 .replace(exp, replace)

replace method

 JS 8 10

A string method that consumes a regular expression and replacement string and produces the string formed by replacing each substring matching the pattern by the replacement string.
157 (a|b)

pattern a or b

 JS 8 12

Used in a regular expression for either string a or string b.
158 [a3]

pattern any character

 JS 8 12

Used in a regular expression for any character in the brackets.
159 [3-5]

pattern character range

 JS 8 12

Used in a regular expression for any character in the range.
160 \d

pattern digit

 JS 8 12

Used in a regular expression for any digit.
161 \s

pattern white space

 JS 8 12

Used in a regular expression for white space.
162 \b

pattern match at beginning or ending

 JS 8 12

Used in a regular expression to show that the match is at the beginning or ending.
163 +

pattern at least one

 JS 8 12

Used in a regular expression to indicate at least of what comes before.
164 *

pattern zero or more

 JS 8 12

Used in a regular expression to indicate zero or more of what comes before.
165 ?

pattern zero or one

 JS 8 12

Used in a regular expression to indicate zero or one of what comes before.