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:
Changing content of a DOM Element:
document.getElementById("elementID").innerHTML = "Hello World!";
This will print the value of a in JavaScript console:
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 (initialization; condition; incrementation;) {
// code block to be executed
}
for (let i = 0; i < 5; i++) {
text += "Iteration number: " + i + "
";
}
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()
Returns the relevant Number Object holding the value of the argument passed:
valueOf()
JS math and number objects provide several constants 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 the code block and execute catch when err is thrown:
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.codewithharry.com");
Prompts the user with a text and takes a value. Second parameter is the default value: