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>
External JS File
Adding external JavaScript to HTML
<script src="filename.js"></script>
Functions
JavaScript Function syntax
function nameOfFunction ()
{
// function body
}
DOM Element
Changing content of a DOM Element
document.getElementById("elementID").innerHTML = "Hello World!";
Output
This will print the value of a in JavaScript console
console.log(a);
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
}
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
}
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
}
Switch Statement
Switch case statement in JavaScript
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
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
}
While Loop
Runs the code till the specified condition is true
while (condition) {
// code block to be executed
}
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);
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)
concat method
Joins two or more strings together.
str1.concat(str2)
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')
match method
Searches a string for a match against a regular expression.
str.match(/(chapter \d+(\.\d)*)/i;)
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)
search method
Searches a string against a specified value.
str.search('term')
split method
Splits a string into an array consisting of substrings.
str.split('\n')
substring method
Returns a substring of a string containing characters from the specified indices.
str.substring(0,5)
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"];
concat method
Joins two or more arrays together.
concat()
indexOf method
Returns the index of the specified item from the array.
indexOf()
join method
Converts the array elements to a string.
join()
pop method
Deletes the last element of the array.
pop()
reverse method
This method reverses the order of the array elements.
reverse()
sort method
Sorts the array elements in a specified manner.
sort()
toString method
Converts the array elements to a string.
toString()
valueOf method
returns the relevant Number Object holding the value of the argument passed
valueOf()
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()
toPrecision method
Formats a number into a specified length.
toPrecision()
toString method
Converts an object to a string
toString()
valueOf method
Returns the primitive value of a number.
valueOf()
Maths Methods
ceil method
Rounds a number upwards to the nearest integer, and returns the result
ceil(x)
exp method
Returns the value of E^x.
exp(x)
log method
Returns the logarithmic value of x.
log(x)
pow method
Returns the value of x to the power y.
pow(x,y)
random method
Returns a random number between 0 and 1.
random()
sqrt method
Returns the square root of a number x
sqrt(x)
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()
Pulling Day from the Date object
Returns the day from the date object
getDay()
Pulling Hours from the Date object
Returns the hours from the date object
getHours()
Pulling Minutes from the Date object
Returns the minutes from the date object
getMinutes()
Pulling Seconds from the Date object
Returns the seconds from the date object
getSeconds()
Pulling Time from the Date object
Returns the time from the date object
getTime()
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
});
oncontextmenu
Fired when an element is right-clicked
element.addEventListener('contextmenu', ()=>{
// Code to be executed when the event is fired
});
dblclick
Fired when an element is double-clicked
element.addEventListener('dblclick', ()=>{
// Code to be executed when the event is fired
});
mouseenter
Fired when an element is entered by the mouse arrow
element.addEventListener('mouseenter', ()=>{
// Code to be executed when the event is fired
});
mouseleave
Fired when an element is exited by the mouse arrow
element.addEventListener('mouseleave', ()=>{
// Code to be executed when the event is fired
});
mousemove
Fired when the mouse is moved inside the element
element.addEventListener('mousemove', ()=>{
// Code to be executed when the event is fired
});
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
});
keypress
Fired when the user presses the key on the keyboard
element.addEventListener('keypress', ()=>{
// Code to be executed when the event is fired
});
keyup
Fired when the user releases a key on the keyboard
element.addEventListener('keyup', ()=>{
// Code to be executed when the event is fired
});
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
}
Window Methods
Methods that are available from the window object
alert method
Used to alert something on the screen
alert()
blur method
The blur() method removes focus from the current window.
blur()
setInterval
Keeps executing code at a certain interval
setInterval(() => {
// Code to be executed
}, 1000);
setTimeout
Executes the code after a certain interval of time
setTimeout(() => {
// Code to be executed
}, 1000);
close
The Window. close() method closes the current window
window.close()
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?')
open
Opens a new window
window.open("https://www.google.com");
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");
scrollBy
window.scrollBy(100, 0); // Scroll 100px to the right
scrollTo
Scrolls the document to the specified coordinates.
window.scrollTo(500, 0); // Scroll to horizontal position 500
clearInterval
Clears the setInterval. var is the value returned by setInterval call
clearInterval(var)
clearTimeout
Clears the setTimeout. var is the value returned by setTimeout call
clearTimeout(var)
stop
Stops the further resource loading
stop()
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')
querySelectorAll
A selector to select all matching elements
document.querySelectorAll('css-selectors', ...)
getElementsByTagName
Select elements by tag name
document.getElementsByTagName('element-name')
getElementsByClassName
Select elements by class name
document.getElementsByClassName('class-name')
Get Element by Id
Select an element by its id
document.getElementById('id')
Creating Elements
Create new elements in the DOM
createElement
Create a new element
document.createElement('div')
createTextNode
Create a new text node
document.createTextNode('some text here')
Download this cheatsheet here
Top comments (3)
This is great. Various Event handling methods & dom manipulation at one place, was wonderful idea.
appreciate the effort! thanks a lot!
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