Javascript Cheat Sheet

Question	Answer
Including JavaScript in an HTML Page	<script type="text/javascript"> //JS code goes here </script>
Call an External JavaScript File	<script src="myscript.js"></script><code></code> Including Comments Single line comments - // Multi-line comments - /* comment here */
var, const, let	var — The most common variable. Can be reassigned but only accessed within a function. Variables defined with var move to the top when code is executed. const — Can not be reassigned and not accessible before they appear within the code. let — Similar to const, however, let variable can be reassigned but not re-declared.
Data Types	Numbers — var age = 23 Variables — var x Text (strings) — var a = "init" Operations — var b = 1 + 2 + 3 True or fase statements — var c = true Constant numbers — const PI = 3.14 Objects — var name = {firstName:"John", lastName:”Doe"}
Data Types	A letter such as 'A' is a character A word/phrase like 'Hello' is a string A number e.g. '2' is an integer A decimal like '2.9' is real 'yes/no' is Boolean A phone number '07543988157' is a STRING
Objects	var person = { firstName:"John", lastName:"Doe", age:20, nationality:"German" };
Array Methods	concat() — Join several arrays into one indexOf() — Returns the primitive value of the specified object join() — Combine elements of an array into a single string and return the string lastIndexOf() — Gives the last position at which a given element appears in an array pop() — Removes the last element of an array push() — Add a new element at the end reverse() — Sort elements in descending order shift() — Remove the first element of an array slice() — Pulls a copy of a portion of an array into a new array sort() — Sorts elements alphabetically splice() — Adds elements in a specified way and position toString() — Converts elements to strings unshift() — Adds a new element to the beginning valueOf() — Returns the first position at which a given element appears in an array
Basic Operators	+ — Addition - — Subtraction * — Multiplication / — Division (...) — Grouping operator, operations within brackets are executed earlier than those outside % — Modulus (remainder ) ++ — Increment numbers -- — Decrement numbers
Comparison Operators	== — Equal to === — Equal value and equal type != — Not equal !== — Not equal value or not equal type > — Greater than < — Less than >= — Greater than or equal to <= — Less than or equal to ? — Ternary operator
Logical Operators	&& — Logical and \|\| — Logical or ! — Logical not
Bitwise Operators	& — AND statement \| — OR statement ~ — NOT ^ — XOR << — Left shift >> — Right shift >>> — Zero fill right shift
FUNCTIONS	function name(parameter1, parameter2, parameter3) { // what the function does }
Outputting Data	alert() — Output data in an alert box in the browser window confirm() — Opens up a yes/no dialog and returns true/false depending on user click console.log() — Writes information to the browser console, good for debugging purposes document.write() — Write directly to the HTML document prompt() — Creates an dialogue for user input
Global Functions	decodeURI() — Decodes a Uniform Resource Identifier (URI) created by encodeURI or similar decodeURIComponent() — Decodes a URI component encodeURI() — Encodes a URI into UTF-8 encodeURIComponent() — Same but for URI components eval() — Evaluates JavaScript code represented as a string isFinite() — Determines whether a passed value is a finite number isNaN() — Determines whether a value is NaN or not Number() — Returns a number converted from its argument parseFloat() — Parses an argument and returns a floating point number parseInt() — Parses its argument and returns an integer
JAVASCRIPT LOOPS	for (before loop; condition for loop; execute after loop) { // what to do during the loop } for — The most common way to create a loop in JavaScript while — Sets up conditions under which aloop executes do while — Similar to the while loop, however, it executes at least once and performs a check at the end to see if the condition is met to execute again break — Used to stop and exit the cycle at certain conditions continue — Skip parts of the cycle if certain conditions are met
IF - ELSE STATEMENTS	if (condition) { // what to do if condition is met } else { // what to do if condition is not met }
STRINGS	var person = "John Doe";
Escape Characters	\' — Single quote \" — Double quote \\ — Backslash \b — Backspace \f — Form feed \n — New line \r — Carriage return \t — Horizontal tabulator \v — Vertical tabulator
String Methods	charAt() — Returns a character at a specified position inside a string charCodeAt() — Gives you the unicode of character at that position concat() — Concatenates (joins) two or more strings into one fromCharCode() — Returns a string created from the specified sequence of UTF-16 code units indexOf() — Provides the position of the first occurrence of a specified text within a string lastIndexOf() — Same as indexOf() but with the last occurrence, searching backwards match() — Retrieves the matches of a string against a search pattern replace() — Find and replace specified text in a string search() — Executes a search for a matching text and returns its position slice() — Extracts a section of a string and returns it as a new string split() — Splits a string object into an array of strings at a specified position substr() — Similar to slice() but extracts a substring depended on a specified number of characters substring() — Also similar to slice() but can’t accept negative indices toLowerCase() — Convert strings to lower case toUpperCase() — Convert strings to upper case valueOf() — Ret
REGULAR EXPRESSION SYNTAX Pattern Modifiers	e — Evaluate replacement i — Perform case-insensitive matching g — Perform global matching m — Perform multiple line matching s — Treat strings as single line x — Allow comments and whitespace in pattern U — Ungreedy pattern
Brackets	[abc] — Find any of the characters between the brackets [^abc] — Find any character not in the brackets [0-9] — Used to find any digit from 0 to 9 [A-z] — Find any character from uppercase A to lowercase z (a\|b\|c) — Find any of the alternatives separated with \|
Metacharacters	. — Find a single character, except newline or line terminator \w — Word character \W — Non-word character \d — A digit \D — A non-digit character \s — Whitespace character \S — Non-whitespace character \b — Find a match at the beginning/end of a word \B — A match not at the beginning/end of a word \0 — NUL character \n — A new line character \f — Form feed character \r — Carriage return character \t — Tab character \v — Vertical tab character \xxx — The character specified by an octal number xxx \xdd — Character specified by a hexadecimal number dd \uxxxx — The Unicode character specified by a hexadecimal number xxxx
Quantifiers	n+ — Matches any string that contains at least one n n* — Any string that contains zero or more occurrences of n n? — A string that contains zero or one occurrences of n n{X} — String that contains a sequence of X n’s n{X,Y} — Strings that contains a sequence of X to Y n’s n{X,} — Matches any string that contains a sequence of at least X n’s n$ — Any string with n at the end of it ^n — String with n at the beginning of it ?=n — Any string that is followed by a specific string n ?!n — String that is not followed by a specific string n
Number Properties	MAX_VALUE — The maximum numeric value representable in JavaScript MIN_VALUE — Smallest positive numeric value representable in JavaScript NaN — The “Not-a-Number” value NEGATIVE_INFINITY — The negative Infinity value POSITIVE_INFINITY — Positive Infinity value
Number Methods	toExponential() — Returns a string with a rounded number written as exponential notation toFixed() — Returns the string of a number with a specified number of decimals toPrecision() — String of a number written with a specified length toString() — Returns a number as a string valueOf() — Returns a number as a number
Math Properties	E — Euler’s number LN2 — The natural logarithm of 2 LN10 — Natural logarithm of 10 LOG2E — Base 2 logarithm of E LOG10E — Base 10 logarithm of E PI — The number PI SQRT1_2 — Square root of 1/2 SQRT2 — The square root of 2
Math Methods	abs(x) — Returns the absolute (positive) value of x acos(x) — The arccosine of x, in radians asin(x) — Arcsine of x, in radians atan(x) — The arctangent of x as a numeric value atan2(y,x) — Arctangent of the quotient of its arguments ceil(x) — Value of x rounded up to its nearest integer cos(x) — The cosine of x (x is in radians) exp(x) — Value of Ex floor(x) — The value of x rounded down to its nearest integer log(x) — The natural logarithm (base E) of x max(x,y,z,...,n) — Returns the number with the highest value min(x,y,z,...,n) — Same for the number with the lowest value pow(x,y) — X to the power of y random() — Returns a random number between 0 and 1 round(x) — The value of x rounded to its nearest integer sin(x) — The sine of x (x is in radians) sqrt(x) — Square root of x tan(x) — The tangent of an angle
Setting Dates	Date() — Creates a new date object with the current date and time Date(2017, 5, 21, 3, 23, 10, 0) — Create a custom date object. The numbers represent year, month, day, hour, minutes, seconds, milliseconds. You can omit anything you want except for year and month. Date("2017-06-23") — Date declaration as a string
Pulling Date and Time Values	getDate() — Get the day of the month as a number (1-31) getDay() — The weekday as a number (0-6) getFullYear() — Year as a four digit number (yyyy) getHours() — Get the hour (0-23) getMilliseconds() — The millisecond (0-999) getMinutes() — Get the minute (0-59) getMonth() — Month as a number (0-11) getSeconds() — Get the second (0-59) getTime() — Get the milliseconds since January 1, 1970 getUTCDate() — The day (date) of the month in the specified date according to universal time (also available for day, month, fullyear, hours, minutes etc.) parse — Parses a string representation of a date, and returns the number of milliseconds since January 1, 1970
Set Part of a Date	setDate() — Set the day as a number (1-31) setFullYear() — Sets the year (optionally month and day) setHours() — Set the hour (0-23) setMilliseconds() — Set milliseconds (0-999) setMinutes() — Sets the minutes (0-59) setMonth() — Set the month (0-11) setSeconds() — Sets the seconds (0-59) setTime() — Set the time (milliseconds since January 1, 1970) setUTCDate() — Sets the day of the month for a specified date according to universal time (also available for day, month, fullyear, hours, minutes etc.)
Node Properties	attributes — Returns a live collection of all attributes registered to and element baseURI — Provides the absolute base URL of an HTML element childNodes — Gives a collection of an element’s child nodes firstChild — Returns the first child node of an element lastChild — The last child node of an element nextSibling — Gives you the next node at the same node tree level nodeName — Returns the name of a node nodeType — Returns the type of a node nodeValue — Sets or returns the value of a node ownerDocument — The top-level document object for this node parentNode — Returns the parent node of an element previousSibling — Returns the node immediately preceding the current one textContent — Sets or returns the textual content of a node and its descendants
Node Methods	appendChild() — Adds a new child node to an element as the last child node cloneNode() — Clones an HTML element compareDocumentPosition() — Compares the document position of two elements getFeature() — Returns an object which implements the APIs of a specified feature hasAttributes() — Returns true if an element has any attributes, otherwise false hasChildNodes() — Returns true if an element has any child nodes, otherwise false insertBefore() — Inserts a new child node before a specified, existing child node isDefaultNamespace() — Returns true if a specified namespaceURI is the default, otherwise false isEqualNode() — Checks if two elements are equal isSameNode() — Checks if two elements are the same node isSupported() — Returns true if a specified feature is supported on the element lookupNamespaceURI() — Returns the namespaceURI associated with a given node lookupPrefix() — Returns a DOMString containing the prefix for a given namespaceURI, if present normalize() — Joins adjacent text nodes and removes empty text nodes in an element removeChild() — Removes a child node from an elem
Element Methods	getAttribute() — Returns the specified attribute value of an element node getAttributeNS() — Returns string value of the attribute with the specified namespace and name getAttributeNode() — Gets the specified attribute node getAttributeNodeNS() — Returns the attribute node for the attribute with the given namespace and name getElementsByTagName() — Provides a collection of all child elements with the specified tag name getElementsByTagNameNS() — Returns a live HTMLCollection of elements with a certain tag name belonging to the given namespace hasAttribute() — Returns true if an element has any attributes, otherwise false hasAttributeNS() — Provides a true/false value indicating whether the current element in a given namespace has the specified attribute removeAttribute() — Removes a specified attribute from an element removeAttributeNS() — Removes the specified attribute from an element within a certain namespace removeAttributeNode() — Takes away a specified attribute node and returns the removed node setAttribute() — Sets or changes the specified attribute to a specified value setA

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Javascript Cheat Sheet

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