function doesn't work

Question

I need a little help with this function:

function passar() { 
 var fotos1 = document.getElementById("foto1");
 var fotos2 = document.getElementById("foto2");
 var fotos3 = document.getElementById("foto3");
 if ( fotos1.style.display = "block" ) { 
 fotos1.style.display = "none"; 
 fotos2.style.display = "block"; 
 } else if ( fotos2.style.display = "block" ) { 
 fotos2.style.display = "none"; 
 } 
} 

It was supposed to hide "fotos 2" when the first condition is changed but it didn't work, someone knows why?

• jbabey: i'm kind of upset that not a single person has said to use the identity operator === ...
• jbabey: == and != is one of the main reasons that the code quality of javascript is as low as it is... use === and !== instead.
• Eli: I was the only one that gave the answer using === and no one cares. :)

Answer 1

= for assignment

== for comparison

=== for strict comparison

if (fotos1.style.display === "block") { 
fotos1.style.display = "none"; 
fotos2.style.display = "block"; 
 } else if (fotos1.style.display === "none") { 
 fotos2.style.display = "none"; 
 } 
} 

• gen_Eric: Other languages have === too :-P

Answer 2

Your conditional statement is doing an assignment rather than a comparison:

if (fotos1.style.display === "block") { 
 fotos1.style.display = "none"; 
 fotos2.style.display = "block"; 
} else if (fotos1.style.display === "none") { 
 fotos2.style.display = "block"; 
}

Also, it is recommended to use strict comparison using === over the weak comparison ==. You get the added benefit of the comparison also being roughly 4X faster in some browsers.

• mayhewr: Didn't realize it was that much faster. Cool.

Answer 3

You should be using a comparison operator which is double equals in this case:

if (fotos1.style.display == "block") {

Instead you are using a single equals which is an assignment parameter:

if (fotos1.style.display = "block") {

• Wiz: Can i know why was this given minus 1?