Set of JavaScript basic syntax to add, execute and write basic programming paradigms in Javascript
Adding internal JavaScript to HTML
<script type="text/javascript"> //JS code goes here </script>
Adding external JavaScript to HTML
<script src="filename.js"></script>
JavaScript Function syntax
function nameOfFunction ()
{
// function body
}
document.getElementById("elementID").innerHTML = "Hello World!";
console.log(a);
Conditional statements are used to perform operations based on some conditions.
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 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
}
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 case statement in JavaScript
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
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 syntax in javascript
for (statement 1; statement 2; statement 3) {
// code block to be executed
}
Runs the code till the specified condition is true
while (condition) {
// code block to be executed
}
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);
The string is a sequence of characters that is used for storing and managing text data.
Returns the character from the specified index.
str.charAt(3)
Joins two or more strings together.
str1.concat(str2)
Returns the index of the first occurrence of the specified character from the string else -1 if not found.
str.indexOf('substr')
Searches a string for a match against a regular expression.
str.match(/(chapter \d+(\.\d)*)/i;)
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)
Searches a string against a specified value.
str.search('term')
Splits a string into an array consisting of substrings.
str.split('\n')
Returns a substring of a string containing characters from the specified indices.
str.substring(0,5)
The array is a collection of data items of the same type. In simple terms, it is a variable that contains multiple values.
Containers for storing data.
var fruit = ["element1", "element2", "element3"];
Joins two or more arrays together.
concat()
Returns the index of the specified item from the array.
indexOf()
Converts the array elements to a string.
join()
Deletes the last element of the array.
pop()
This method reverses the order of the array elements.
reverse()
Sorts the array elements in a specified manner.
sort()
Converts the array elements to a string.
toString()
valueOf()
JS math and number objects provide several constant and methods to perform mathematical operations.
Converts a number to its exponential form.
toExponential()
Formats a number into a specified length.
toPrecision()
Converts an object to a string
toString()
Returns the primitive value of a number.
valueOf()
Rounds a number upwards to the nearest integer, and returns the result
ceil(x)
Returns the value of E^x.
exp(x)
Returns the logarithmic value of x.
log(x)
Returns the value of x to the power y.
pow(x,y)
Returns a random number between 0 and 1.
random()
Returns the square root of a number x
sqrt(x)
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.
Returns the date from the date object
getDate()
Returns the day from the date object
getDay()
Returns the hours from the date object
getHours()
Returns the minutes from the date object
getMinutes()
Returns the seconds from the date object
getSeconds()
Returns the time from the date object
getTime()
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.
Fired when an element is clicked
element.addEventListener('click', ()=>{
// Code to be executed when the event is fired
});
Fired when an element is right-clicked
element.addEventListener('contextmenu', ()=>{
// Code to be executed when the event is fired
});
Fired when an element is double-clicked
element.addEventListener('dblclick', ()=>{
// Code to be executed when the event is fired
});
Fired when an element is entered by the mouse arrow
element.addEventListener('mouseenter', ()=>{
// Code to be executed when the event is fired
});
Fired when an element is exited by the mouse arrow
element.addEventListener('mouseleave', ()=>{
// Code to be executed when the event is fired
});
Fired when the mouse is moved inside the element
element.addEventListener('mousemove', ()=>{
// Code to be executed when the event is fired
});
Fired when the user is pressing a key on the keyboard
element.addEventListener('keydown', ()=>{
// Code to be executed when the event is fired
});
Fired when the user presses the key on the keyboard
element.addEventListener('keypress', ()=>{
// Code to be executed when the event is fired
});
Fired when the user releases a key on the keyboard
element.addEventListener('keyup', ()=>{
// Code to be executed when the event is fired
});
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 {
Block of code to try
}
catch(err) {
Block of code to handle errors
}
Methods that are available from the window object
Used to alert something on the screen
alert()
The blur() method removes focus from the current window.
blur()
Keeps executing code at a certain interval
setInterval(() => {
// Code to be executed
}, 1000);
Executes the code after a certain interval of time
setTimeout(() => {
// Code to be executed
}, 1000);
The Window. close() method closes the current window
window.close()
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?')
Opens a new window
window.open("https://www.google.com");
Prompts the user with a text and takes a value. Second parameter is the default value
var name = prompt("What is your name?", "Abhiraj");
window.scrollBy(100, 0); // Scroll 100px to the right
Scrolls the document to the specified coordinates.
window.scrollTo(500, 0); // Scroll to horizontal position 500
clearInterval(var)
clearTimeout(var)
stop()
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.
Selector to select first matching element
document.querySelector('css-selectors')
A selector to select all matching elements
document.querySelectorAll('css-selectors', ...)
Select elements by tag name
document.getElementsByTagName('element-name')
Select elements by class name
document.getElementsByClassName('class-name')
Select an element by its id
document.getElementById('id')
Create new elements in the DOM
createElement
document.createElement('div')
Create a new text node
document.createTextNode('some text here')