Parameter Test

updated by JMH on September 19, 2009 at 7:09 PM
updated by JMH on October 4, 2015 at 11:55 AM
updated by JMH on May 19, 2023 at 8:19 PM


Function definition:

function test( a, b, c )
or
var test = function( a, b, c )

Executing JavaScript function call:

test( 1, "one" ) ;

Results:

Referencing parameter a   returns   1
Referencing parameter b   returns   one
Referencing parameter c   returns   undefined
 
c == null   returns   true
c === null   returns   false

c == undefined   returns   true   because undefined is a built-in VALUE
c === undefined   returns   true

c == "undefined"   returns   false   because undefined is NOT a STRING
c === "undefined"   returns   false

Testing typeof as an operator:

typeof c   returns   undefined   as a STRING
typeof c == "undefined"   returns   true
typeof c === "undefined"   returns   true
typeof c == undefined   returns   false   because typeof returns a STRING
typeof c === undefined   returns   false

Testing typeof as a function:

typeof( c )   returns   undefined   as a STRING
typeof( c ) == "undefined"   returns   true
typeof( c ) === "undefined"   returns   true
typeof( c ) == undefined   returns   false   because typeof(...) returns a STRING
typeof( c ) === undefined   returns   false