JavaScript/CheatSheet
Style guides
Comments
// single-line comment /* multi-line comment */
Data Types
var num = 8; // number var strg = "Joe"; // string var vobj = {first: "John", last:"Doe"}; // object var booli = false; // boolean var arr = ["HTML","CSS","JS"]; // array var a; typeof a; // undefined var a = null; // value null const pi = 3.14; typeof strg // =string
Arrays
var title = new Array(); title[0] = "Mr."; title[1] = "Mrs."; element = title.slice(-1);
- Methods
concat() both = array1.concat(array2) # joins two or more arrays join() text = array.join() # joins array to form one long string map() newAr = array.map(Math.sqrt) # return a new array after function pop() # remove last element shift() # remove first element unshift() # add new element to beginning push() # add new element to end reduce() reverse() # reverse the order of elements slice() array,slice(start, end) splice() array.splice(position, numRemove, "New"); # at position, remove n-elements and insert new elements forEach() array.forEach(function) # calls a function for each element sort() filter()
- Properties
length
Objects (key : value)
var user = { firstname: "Peter", lastname: "Johnson" } user.phone = "01234"
user.firstname user["firstname"]
var result = arrayName.filter(obj => { return obj.key === value })
Strings
charAt() charCodeAt() concat() fromCharCode() indexOf() lastIndexOf() match() replace() zpl = zpl.replace("1234567890",msg.serialnumber) search() slice() checksum = String(sum).slice(-1) # get last digit split() substr() substring() toLowerCase() toUpperCase() valueOf() trim() remove whitespace from both sides trimStart() trimEnd() includes() if (string.includes(".prn")) {}
sinngle-quote var str = 'test' // use single-quotes for strings back-tick var str = `text and ${variable}` // use back-ticks when multiline or interpolation double-quote var str = "test"
- Remove ANSI colors from string
payload = payload.replace(/[\u001b\u009b][[()#;?]*(?:[0-9]{1,4}(?:;[0-9]{0,4})*)?[0-9A-ORZcf-nqry=><]/g, '');
- add leading zeros
var string = "000000" + integer.toString() string = string.substr(string.length-6)
Conversions
string = integer.toString() # integer -> string String(123) # integer -> string toExponential() toFixed() toPrecision() integer = parseInt(string) + 1 # string -> integer float = parseFloat(string) # string -> float jsonvar = JSON.parse(string) # string -> json number = Number("1.23") # string -> number
- Date & Time
dt = new Date(); Number(dt) # date -> number dt.getTime() # date -> number String(dt) # date -> string dt.toString() # date -> string
Functions
function addition(number1, number2) { return number1 + number2; } var person = { name: 'Peter', getName: function () { return this.name; } } person.getName()
Operators
+ Addition - Subtraction * Multiplication / Division (...) Grouping operator, operations within brackets are executed earlier than those outside % Modulus (remainder ) ++ Increment numbers -- Decrement numbers == 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 and || Logical or ! Logical not & AND statement | OR statement ~ NOT ^ XOR << Left shift >> Right shift >>> Zero fill right shift
if - else
if (condition) { // if condition is met } else { // if condition is not met }
switch
switch(var) { case 1: // code break; case 2: // code break; default: // code }
Loops
for (var i = 0; i < 10; i++){ } while (i < 10) { i++; } do { i++; } while (i < 10); break continue
Escape Characters
\' Single quote \" Double quote \\ Backslash \b Backspace \f Form feed \n New line \r Carriage return \t Horizontal tabulator \v Vertical tabulator
Dates & Times
d = new Date(); var year = d.getFullYear(); var month = d.getMonth() + 1;
function ISO8601_week_no() { dt = new Date(); var tdt = new Date(dt.valueOf()); var dayn = (dt.getDay() + 6) % 7; tdt.setDate(tdt.getDate() - dayn + 3); var firstThursday = tdt.valueOf(); tdt.setMonth(0, 1); if (tdt.getDay() !== 4) { tdt.setMonth(0, 1 + ((4 - tdt.getDay()) + 7) % 7); } return 1 + Math.ceil((firstThursday - tdt) / 604800000); }
Random
Math.random(); float (0.0 - 1.0) Math.floor(Math.random() * 10); int (0 - 9) Math.floor(Math.random() * 11); int (0 - 10) Math.floor(Math.random() * (max - min) ) + min;