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Abhiraj Bhowmick
Abhiraj Bhowmick

Posted on • Originally published at abhirajbhowmick.hashnode.dev

The Ultimate Javascript Cheatsheet

JavaScript Basics

Set of JavaScript basic syntax to add, execute and write basic programming paradigms in Javascript

On Page Script

Adding internal JavaScript to HTML

<script type="text/javascript"> //JS code goes here </script>
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External JS File

Adding external JavaScript to HTML

<script src="filename.js"></script>
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Functions

JavaScript Function syntax

function nameOfFunction () 
{
// function body 
}
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DOM Element

Changing content of a DOM Element

document.getElementById("elementID").innerHTML = "Hello World!";
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Output
This will print the value of a in JavaScript console

console.log(a);
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Conditional Statements

Conditional statements are used to perform operations based on some conditions.

If Statement
The block of code to be executed, when the condition specified is true.

if (condition) {
// block of code to be executed if the condition is true
}
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If-else Statement
If the condition for the if block is false, then the else block will be executed.

if (condition) {
// block of code to be executed if the condition is true
} else {
// block of code to be executed if the condition is false
}
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Else-if Statement
A basic if-else ladder

if (condition1) {
// block of code to be executed if condition1 is true
} else if (condition2) {
// block of code to be executed if the condition1 is false and condition2 is true
} else {
// block of code to be executed if the condition1 is false and condition2 is false
}
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Switch Statement
Switch case statement in JavaScript

switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
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Iterative Statements (Loops)

Iterative statement facilitates programmer to execute any block of code lines repeatedly and can be controlled as per conditions added by the programmer.

For Loop
For loop syntax in javascript

for (statement 1; statement 2; statement 3) {
// code block to be executed
}
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While Loop
Runs the code till the specified condition is true

while (condition) {
// code block to be executed
}
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Do While Loop
A do while loop is executed at least once despite the condition being true or false

do {
// run this code in block
i++;
} while (condition);
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Strings

The string is a sequence of characters that is used for storing and managing text data.

charAt method
Returns the character from the specified index.

str.charAt(3)
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concat method
Joins two or more strings together.

str1.concat(str2)
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index of method
Returns the index of the first occurrence of the specified character from the string else -1 if not found.

str.indexOf('substr')
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match method
Searches a string for a match against a regular expression.

str.match(/(chapter \d+(\.\d)*)/i;)
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replace method
Searches a string for a match against a specified string or char and returns a new string by replacing the specified values.

str1.replace(str2)
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search method
Searches a string against a specified value.

str.search('term')
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split method
Splits a string into an array consisting of substrings.

str.split('\n')
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substring method
Returns a substring of a string containing characters from the specified indices.

str.substring(0,5)
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Arrays

The array is a collection of data items of the same type. In simple terms, it is a variable that contains multiple values.

variable
Containers for storing data.

var fruit = ["element1", "element2", "element3"];
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concat method
Joins two or more arrays together.

concat()
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indexOf method
Returns the index of the specified item from the array.

indexOf()
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join method
Converts the array elements to a string.

join()
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pop method
Deletes the last element of the array.

pop()
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reverse method
This method reverses the order of the array elements.

reverse()
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sort method
Sorts the array elements in a specified manner.

sort()
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toString method
Converts the array elements to a string.

toString()
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valueOf method
returns the relevant Number Object holding the value of the argument passed

valueOf()
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Number Methods

JS math and number objects provide several constant and methods to perform mathematical operations.

toExponential method
Converts a number to its exponential form.

toExponential()
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toPrecision method
Formats a number into a specified length.

toPrecision()
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toString method
Converts an object to a string

toString()
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valueOf method
Returns the primitive value of a number.

valueOf()
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Maths Methods

ceil method
Rounds a number upwards to the nearest integer, and returns the result

ceil(x)
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exp method
Returns the value of E^x.

exp(x)
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log method
Returns the logarithmic value of x.

log(x)
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pow method
Returns the value of x to the power y.

pow(x,y)
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random method
Returns a random number between 0 and 1.

random()
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sqrt method
Returns the square root of a number x

sqrt(x)
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Dates

Date object is used to get the year, month and day. It has methods to get and set day, month, year, hour, minute, and seconds.

Pulling Date from the Date object
Returns the date from the date object

getDate()
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Pulling Day from the Date object
Returns the day from the date object

getDay()
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Pulling Hours from the Date object
Returns the hours from the date object

getHours()
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Pulling Minutes from the Date object
Returns the minutes from the date object

getMinutes()
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Pulling Seconds from the Date object
Returns the seconds from the date object

getSeconds()
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Pulling Time from the Date object
Returns the time from the date object

getTime()
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Mouse Events

Any change in the state of an object is referred to as an Event. With the help of JS, you can handle events, i.e., how any specific HTML tag will work when the user does something.

click
Fired when an element is clicked

element.addEventListener('click', ()=>{
// Code to be executed when the event is fired
});
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oncontextmenu
Fired when an element is right-clicked

element.addEventListener('contextmenu', ()=>{
// Code to be executed when the event is fired
});
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dblclick
Fired when an element is double-clicked

element.addEventListener('dblclick', ()=>{
// Code to be executed when the event is fired
});
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mouseenter
Fired when an element is entered by the mouse arrow

element.addEventListener('mouseenter', ()=>{
// Code to be executed when the event is fired
});
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mouseleave
Fired when an element is exited by the mouse arrow

element.addEventListener('mouseleave', ()=>{
// Code to be executed when the event is fired
});
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mousemove
Fired when the mouse is moved inside the element

element.addEventListener('mousemove', ()=>{
// Code to be executed when the event is fired
});
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Keyboard Events
keydown
Fired when the user is pressing a key on the keyboard

element.addEventListener('keydown', ()=>{
// Code to be executed when the event is fired
});
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keypress
Fired when the user presses the key on the keyboard

element.addEventListener('keypress', ()=>{
// Code to be executed when the event is fired
});
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keyup
Fired when the user releases a key on the keyboard

element.addEventListener('keyup', ()=>{
// Code to be executed when the event is fired
});
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Errors

Errors are thrown by the compiler or interpreter whenever they find any fault in the code, and it can be of any type like syntax error, run-time error, logical error, etc. JS provides some functions to handle the errors.

try and catch
Try the code block and execute catch when err is thrown

try {
Block of code to try
}
catch(err) {
Block of code to handle errors
}
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Window Methods
Methods that are available from the window object

alert method
Used to alert something on the screen

alert()
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blur method
The blur() method removes focus from the current window.

blur()
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setInterval
Keeps executing code at a certain interval

setInterval(() => {
// Code to be executed
}, 1000);
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setTimeout
Executes the code after a certain interval of time

setTimeout(() => {
// Code to be executed
}, 1000);
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close
The Window. close() method closes the current window

window.close()
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confirm
The window.confirm() instructs the browser to display a dialog with an optional message, and to wait until the user either confirms or cancels

window.confirm('Are you sure?')
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open
Opens a new window

window.open("https://www.google.com");
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prompt
Prompts the user with a text and takes a value. Second parameter is the default value

var name = prompt("What is your name?", "Abhiraj");
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scrollBy

window.scrollBy(100, 0); // Scroll 100px to the right
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scrollTo
Scrolls the document to the specified coordinates.

window.scrollTo(500, 0); // Scroll to horizontal position 500
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clearInterval
Clears the setInterval. var is the value returned by setInterval call

clearInterval(var)
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clearTimeout
Clears the setTimeout. var is the value returned by setTimeout call

clearTimeout(var)
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stop
Stops the further resource loading

stop()
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Query/Get Elements

The browser creates a DOM (Document Object Model) whenever a web page is loaded, and with the help of HTML DOM, one can access and modify all the elements of the HTML document.

querySelector
Selector to select first matching element

document.querySelector('css-selectors')
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querySelectorAll
A selector to select all matching elements

document.querySelectorAll('css-selectors', ...)
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getElementsByTagName
Select elements by tag name

document.getElementsByTagName('element-name')
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getElementsByClassName
Select elements by class name

document.getElementsByClassName('class-name')
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Get Element by Id
Select an element by its id

document.getElementById('id')
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Creating Elements
Create new elements in the DOM

createElement
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Create a new element

document.createElement('div')
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createTextNode
Create a new text node

document.createTextNode('some text here')
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Download this cheatsheet here

Discussion (4)

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lukeshiru profile image
LUKESHIRU

A few extras:

  • On Page Script: You don't actually need type="text/javascript", so you can simply do:
<script></script>
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  • Functions: There are actually several different ways of writing functions:
function nameOfFunction() {
    // function body
}

const nameOfFunction = function () {
    // function body
};

const nameOfFunction = () => {
    // function body
};

const nameOfFunction = argument => returnValue;

(function () {
    // IIFE
})();

(() => {
    // Arrow IIFE
})();
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  • Changing content of a DOM Element: You can (and ideally should) change the content of a DOM element using textContent as well:
document.querySelector("element").textContent = `
    If we put HTML here it will not
    be parsed as such (which is more secure)
`;
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  • Else-if Statement: Those can be written using blocks, which I believe are bette for readability:
if (condition1) {
    // block of code to be executed if condition1 is true
} else {
    if (condition2) {
        // block of code to be executed if the condition1 is false and condition2 is true
    } else {
        // block of code to be executed if the condition1 is false and condition2 is false
    }
}
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  • For Loop: Has other variants far more useful thant the triple statement:
for (const item of array) {
    // loop trough an array, item being the current item
}

for (const prop in object) {
    // loops over an object, property being the property key
}
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  • String.prototype.charAt: You can use char[index] instead.
  • String.prototype.concat: You can do this instead:
`${string1}${string2}`;
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  • String.prototype.replace: There is a typo on that example. The replace method takes 2 arguments, a string or a RegExp first, and then another string or a callback function as a second argument.

  • Variable: For variables nowadays is better to use either let or const, no var.

  • toString: Is actually not exclusive to Array or Number, but the method called to transform to string objects. If you add that method to your own objects and try to parse them as strings, you'll get whatever that function returns.

  • Dates: There is a proposal coming for an alternative to Date called Temporal (you can learn more about it here), but even if you work with Date for now, ideally you should try to use the UTC and the Locale methods, instead of the old ones. So instead of toString, use toLocaleDateString, or instead of getDate use getUTCDate.

  • Mouse events: Consider taking a look at pointer events, which are designed for the current times.

  • Selectors: Having querySelector and querySelectorAll, other methods like getElementsByTagName and getElementById are redundant:

document.querySelectorAll("tag-name"); // instead of document.getElementsByTagName('tag-name');
document.querySelectorAll(".class-name"); // instead of document.getElementsByClassName('class-name');
document.querySelector("#id"); // instead of document.getElementById('id');
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  • Create element: Creating elements with document.createElement works great, until you want to create an SVG element, in such case the syntax looks like this:
document.createElementNS("http://www.w3.org/2000/svg", "svg-element-name");
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That's it, cheers!

PS: Remember that in DEV you can get syntax highlight in the code snippets of your posts by adding the language after the triple back-tick.

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abhirajb profile image
Abhiraj Bhowmick Author

appreciate the effort! thanks a lot!

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prakh_r profile image
Prakhar Yadav

This is great. Various Event handling methods & dom manipulation at one place, was wonderful idea.

p.s. I also learnt somewhere that getElementByClassName is faster than querySelector

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stuffsuggested profile image