Functions in JavaScript

Functions are one of the fundamental building blocks in JavaScript.

  • A function is a JavaScript procedure—a set of statements that performs a task or calculates a value.
  • A JavaScript function is a block of code designed to perform a particular task.
  • A JavaScript function is executed when “something” invokes it (calls it).
JavaScript Function Syntax –

A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses (). Function names can contain letters, digits, underscores, and dollar signs (same rules as variables). The parentheses may include parameter names separated by commas:
(parameter1, parameter2, …)

The code to be executed, by the function, is placed inside curly brackets: {}

  • Function parameters are listed inside the parentheses () in the function definition.
  • Function arguments are the values received by the function when it is invoked.
  • Inside the function, the arguments (the parameters) behave as local variables.
Function Invocation –

The code inside the function will execute when “something” invokes (calls) the function:

  • When an event occurs (when a user clicks a button)
  • When it is invoked (called) from JavaScript code
  • Automatically (self invoked)
Function Return –

When JavaScript reaches a return statement, the function will stop executing. If the function was invoked from a statement, JavaScript will “return” to execute the code after the invoking statement. Functions often compute a return value. The return value is “returned” back to the “caller”:

Output –
Program Example 2 –
Output –
Why Functions?
  • You can reuse code: Define the code once, and use it many times.
  • You can use the same code many times with different arguments, to produce different results.

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