JavaScript Functions Introduction


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). This post is based on w3schools.com’s discussion of JavaScript Functions.

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 the names listed in the function definition.
  • Function arguments are the real values received by the function when it is invoked.

Inside the function, the arguments (the parameters) behave as local variables. A Function is much the same as a Procedure or a Subroutine, in other programming languages.

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”:

var x = multiplyTwoNumbers(4, 3);        // Function is called, return value will end up in x

function multiplyTwoNumbers(a, b) {
    return a * b;                // Function returns the product of a and b, which is 12
}

Notice that we do not specify a type for the two parameters a and b.

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