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A cheatsheet of array methods:

  • To add/remove elements:

    • push(...items) – adds items to the end,
    • pop() – extracts an item from the end,
    • shift() – extracts an item from the beginning,
    • unshift(...items) – adds items to the beginning.
    • splice(pos, deleteCount, ...items) – at index pos delete deleteCount elements and insert items.
    • slice(start, end) – creates a new array, copies elements from position start till end (not inclusive) into it.
    • concat(...items) – returns a new array: copies all members of the current one and adds items to it. If any of itemsis an array, then its elements are taken.
  • To search among elements:

    • indexOf/lastIndexOf(item, pos) – look for item starting from position pos, return the index or -1 if not found.
    • includes(value) – returns true if the array has value, otherwise false.
    • find/filter(func) – filter elements through the function, return first/all values that make it return true.
    • findIndex is like find, but returns the index instead of a value.
  • To transform the array:

    • map(func) – creates a new array from results of calling func for every element.
    • sort(func) – sorts the array in-place, then returns it.
    • reverse() – reverses the array in-place, then returns it.
    • split/join – convert a string to array and back.
    • reduce(func, initial) – calculate a single value over the array by calling func for each element and passing an intermediate result between the calls.
  • To iterate over elements:

    • forEach(func) – calls func for every element, does not return anything.
  • Additionally:

    • Array.isArray(arr) checks arr for being an array.
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Just a little reference to recall syntax of some basic Javascript...

List of useful Basic Syntax

Number(value)  //convert to number *same for objects
Boolean(value)  //convert to boolean
String(value)  //convert to string
toString() & valueOf()  //converting to string or number
Math.floor & Math.ceil & Math.round  //rounding
.toFixed(n)  //returns string so Number() should be used if needed for calculation
isNaN(value) & ifFinite(value), b)  //compare 2 vaues
parseInt() & parseFloat() //returns number from string (until it gets to a NaN)
Math.random()  //Returns a random number from 0 to 1 (not including 1)
Math.max(a, b, c...) & Math.min(a, b, c...)  //Returns the greatest & smallest from the arbitrary number of arguments.
Math.pow(n, power)
Math.sign(x)  //positive, negative or zero
string.length  //length of the string
string[0]  & string.charAt(0)  //first character
string[string.length - 1]  //last character
for (let char of string) {do something}
toLowerCase() & toUpperCase()
string.indexOf(substr, pos)  // pos = start position (optional)  substr = needle, string = haystack
string.lastIndexOf(pos)  // starts at end of string
string.includes(substr, pos)  // pos = starting position (optional)
.startsWith() & .endsWith()
.slice(0, 5)  & .slice(-5, -1)  //returns chunk of string between 0 and 5 characters; negatives work from the end of the string
.substring(a, b)  //returns chunk between 2 positions
.substr(start pos, length)  //start pos can be negative and start from end

arr.splice(index, delete count[, val1, val2, valN]);
arr.splice(start at, number to delete, add value 1, add value 2);
arr.splice(2, 0, "value1", "value2");  //start at position 2, delete none, then insert value 1 & value 2 (at position 2) & also works with negative index
arr.slice(from index, to before position) //works with negs also
arr.indexOf(item, from) //looks for item starting from index from, and returns the index where it was found, otherwise -1.
arr.lastIndexOf(item, from) //same as ^, but looks from right to left.
arr.includes(item, from) //looks for item starting from index from, returns true if found.
let result = arr.find(function(item, index, array)  // should return true if the item is what we are looking for
let result =, index, array) {} // It calls the function for each element of the array and returns the array of results. like:  let lengths = ["Bilbo", "Gandalf", "Nazgul"].map(item => item.length)
arr.sort(); //only works on strings unless you add a function to compare
arr.reverse();  //reverses the order of an array
str.split(delimeter) //let str = "a, b, c"; let arr = str.split(", ") turns string into array like explode in PHP [optional array length as 2nd argument]
arr.join(delimeter); //reverse of split... like PHP implode
Array.isArray(value); //true if value is array
map.set(key, value)  //Probably useless - like array but stores keys of any type (even functions)
map.get(key); map.has(key); map.delete(key); map.clear(); map.size()  //map is just the name of the map in these
map.set('1', 'str1').set(1, 'num1').set(true, 'bool1');  //can be chained - also on new lines for each
new Set(iterable) //has same syntax as map above - only keeps unique values (duplicates thrown out)

Simple function Declaration syntax (can be used anywhere)

function showMessage(msg) {

let xxx = "hello";
showMessage(xxx); // alerts 'hello'

Function expression syntax (can only be used after declared)

let sayHi = function() {

Arrow Functions

let func = (arg1, arg2, ...argN) => expression

let sum = (a, b) => a + b;

same as

let sum = function(a, b) {
    return a + b;


let double = function(n) { return n * 2 }

is the same as...

let double = n => n * 2;

Objects can be either:

let object = {
key1 = value1,
key2 = value2,
keyN = valueN

or similar to PHP (less common)...

let object = new Object();

When using an object, you can do it by either method below... but any variable can be put in square brackets and will be converted

let abc = "key2";
let example = object.key1;
let example = object[key1];
let example = object[abc];  // same as object [key2]

Property values declaration in shorthand... The use-case of making a property from a variable is so common, that there’s a special property value shorthand to make it shorter.

function makeUser(name, age) {
    return {
        name: name,
        age: age
        // ...other properties

Can be written as:

function makeUser(name, age) {
    return {
        // ...other properties
} Loop

for(let key in object) {
    // do something with the keys in loop (ignores symbols);
    continue; // breaks, then continues from beginning of loop
    break; // ends loop

Clone the object, user:

let clone = Object.assign({}, user);

Basic Syntax for assigning both multiple other objects and keys:

Object.assign(dest[, src1, src2, src3...] [,{key = value, keyN = valueN})


let id = Symbol("id");  // "id" is just used as directions/notes - not used at ALL

Global Symbols

let id = Symbol.for("id");

to get the name (remember, name is only used for debugging purposes)

let symbolName = Symbol.keyfor(id);

Shorthand for writing method in function:

let user = {
    name: "John",
    age: 30,
    sayHi() { // same as "sayHi: function()"

Constructor Function

function User(name) { = "John"; 
     this.isAdmin = false;
let user = new User("abc");

let user = new function() {  //one use constructor function = "John";
     this.isAdmin = false;


let arr = new Array();
let arr = [];  //same as above, but more common

let arr = ["nissan", "toyota"];  // arr[1] would be toyota

for (let i = 0; i < 5; i++) {do something} // after 2nd value, undefined
for (let i = 0; i < arr.length; i++) {do something} // works - not shortest but fastest and will skip non-numeric keys
for (let key in arr) {do something}  // much easier but slower and will spit out non-numeric keys

lenghtOfArray = arr.length;

arr.pop //removes last item [fast]
arr.push //append element(s) to end [fast]
arr.shift //extracts 1st element, returns it and removes it [slow]
arr.unshift //add element(s) to beginning [slow]

Multidimensional Arrays

let matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ];
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Note: I've seen this not work - especially with WordPress sites that have caching plugins installed.

<div class="hidden">
<script type="text/javascript">
var images = new Array()
function preload() {
for (i = 0; i < preload.arguments.length; i++) {
images[i] = new Image()
images[i].src = preload.arguments[i]
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Just a little Javascript will do the trick...
        window.onbeforeunload = function(e){
            document.getElementById('idOfElementToChange').className = 'classAddedAfterClick';

 Pretty self-explanatory.  Replace idOfElementToChange with the ID of the element that will incur the new class.  And ClassAddedAfterClick is the new class that will be added.  Probably didn't need to say this.

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Simplest of Simple Javascript Lightbox Scripts...



    display: none;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: black;
    -moz-opacity: 0.8;
    filter: alpha(opacity=80);
.white_content {
    display: none;
    position: absolute;
    top: 15%;
    left: 50%;
    width: 500px;
    height: 580px;
    padding: 16px;
    border: 16px solid #555;
    background-color: white;
    overflow: auto;



<div id="content" class="white_content">
<button style="float:right" onclick = "document.getElementById('content').style.display='none';document.getElementById('fade').style.display='none'">Close</button>
content or image goes here...
<button style="margin-bottom:20px;" onclick = "document.getElementById('content').style.display='none';document.getElementById('fade').style.display='none'">Close</button>
<div id="fade" class="black_overlay"></div>



<a href = "javascript:void(0)" onclick = "document.getElementById('content').style.display='block';document.getElementById('fade').style.display='block'">View Lightbox</a>
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