What is JavaScript ?
- JavaScript is the programming language of the web.
- It is a dynamic scripting language that supports prototype-based object construction.
- Many of the basic syntax and language are constructs that are similar to Java and C++.
Getting JavaScript onto your webpage.
- Write it right on the HTML page.
- Import the JavaScript file:
- <script src="sampleJavaScript.js" type="text/javascript"></script>
Before We Get Started,
- It is important to understand how variables work differently in JavaScript.
Scoping of Variables
- Variables in JavaScript are either considered to be local or global.
- Local Variable Scope :- Local variables can only be created in function.
- There is no such thing as block-level scope variables.
Any variables created in any other block of code (code surrounded by curly brackets) will be considered global.
Example: Variables that are part of an if statement are not local to the if statement, it is considered as a global variable.
Global Variable Scope
- var color = "blue";
- if (color)
- {
- var color = "purple";
- console.log(color);
- }
- console.log(color);
Local Variable Scope
- var color = "blue";
-
- function printColor()
- {
- var color = "purple";
- console.log(color);
- }
- printColor();
- console.log(color);
Though both the local and global variable have the same name, the local variable will take precedence over the global variable in the printColor function.
Functions in JavaScript
- Just like functions in other languages, functions in JavaScript are a block of code used to perform a particular task.
- A function is defined with function keyword, followed by the name of the function and then a pair of parentheses, which will contain the parameters.
- Functions in JavaScript have other capabilities that they do not have in other object oriented languages.
Example:
- var x = 3;
-
- function numSquare(x)
- {
- return x * x;
- }
As we know that function can do different things. Assign one variable result into another variable.
Example 1:
- var x = 3;
-
- function numSquare(x)
- {
- return x * x;
- }
- var sentence = "The Square of " + x + " is equal to " + numSquare(x);
- console.log(sentence);
Output: The Square of 3 is equal to 9
Example 2:
- var num = numSquare(5);
- console.log(num);
Output: 36
Self Invoking Function
- A Special type of function that can be created within JavaScript.
- These functions run automatically. No call to the function needed.
- They can be anonymous or not.
- ((function selfPrint()
- {
- console.log("This function will automatically print this statement);
- })());
-