Question

I come from a C# background and need to become more familiar with JS. I’m reading a book and in this example:

var as = document.getElementsByTagName('a');
for(var i=0;i<as.length;i++){
    t=as[i].className;
    //Check if a link has a class and if the class is the right one
    if(t && t.toString().indexOf(popupClass) != -1)
    {
       //...
    }

Part of the if statement doesn’t make sense. What is if(t)? I am used to if statements checking boolean values, but t is a string, right?

Answer 1

The if statement does type coercion.

if (o) block;

will only run the block. if o is “truthy”

The following values are falsy:

"", null, undefined, false, 0, NaN

The rest are truthy.

A good article can be found here

More to the point you have lots of dead code.

var as = document.getElementsByTagName('a');
for(var i=0;i<as.length;i++){
    t=as[i].className;
    // no need to check for whether t exists. No need to cast it to a string
    if(t.indexOf(popupClass) !== -1) // use !== for strict equality
    {
       //...
    }