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Chapter 2 - Array, Function & String
Part 2
Define Function -:
In JavaScript, a function is a block of code designed to perform a particular task. It is executed when “called” or “invoked.” Functions help you organize your code, make it reusable, and structure it logically.
1. Function Declaration
This is the most common way to define a function. It has the following syntax:
functionName: This is the name you give the function, which is used to call or invoke it.parameters: These are placeholders for values the function can accept when called.code to be executed: The block of code that runs when the function is invoked.
Example:
2. Function Invocation
Once a function is defined, you can call it (or invoke it) by using its name followed by parentheses.
Example:
3. Return Statement
The return statement is used in a function to send a value back to the caller. Once a return statement is executed, the function stops running.
Example:
Function Calling -:
In JavaScript, calling a function means executing the code within the function block. You do this by specifying the function’s name followed by parentheses, optionally passing arguments if the function takes parameters.
Syntax of Calling a Function
To call or invoke a function, you use its name followed by parentheses.
Example of Calling a Function
Function Calling through HTML-:
In HTML, you can call JavaScript functions through various event attributes. These event attributes are typically tied to user interactions like clicks, key presses, form submissions, or even page load events. JavaScript functions can be invoked directly from HTML by using these attributes in the HTML tags.
Here’s a step-by-step guide with examples:
1. Calling a JavaScript Function on Button Click
You can call a JavaScript function when a button is clicked by using the onclick event handler in HTML.
String in Java Script -:
In JavaScript, a string is a sequence of characters used to represent text. Strings are one of the primitive data types in JavaScript, and they are immutable, meaning once created, they cannot be changed (although new strings can be created based on operations performed on existing ones).
1. Declaring Strings
Strings in JavaScript can be declared in three ways:
- Using single quotes (
'). - Using double quotes (
"). - Using backticks (
Example:
All of these declarations create valid string variables. The choice between single or double quotes is typically based on preference or the need to include quotes within the string itself.
2. String Properties
- Length Property: The
.lengthproperty returns the number of characters in the string.
Example:
3. String Methods
JavaScript provides many built-in methods to work with strings. Some of the most common methods include:
3.1. charAt()
Returns the character at a specific index.
3.2. indexOf()
Returns the index of the first occurrence of a substring. If the substring is not found, it returns -1.
3.3. slice()
Extracts a portion of a string and returns it as a new string without modifying the original string.
3.4. substring()
Similar to slice(), but it doesn’t accept negative indices.
3.5. toUpperCase() and toLowerCase()
Converts the string to all uppercase or lowercase letters.
3.6. replace()
Replaces part of the string with another substring. It only replaces the first occurrence by default.
3.7. split()
Splits a string into an array based on a specified separator.
3.8. trim()
Removes whitespace from both ends of a string.
3.9. includes()
Determines whether a string contains a specified substring, returning true or false.
4. Concatenation of Strings
You can join two or more strings together using either:
- The
+operator. - The
concat()method.
Example:
end of part 2 -------->
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Define Function -: