Accessing API with multiple embedded presentations

[jaybonthius]

In the documentation for API Methods, it says

If you're working with a single presentation instance the API can be accessed via the global Reveal object.

But what if I'm working with multiple embedded presentations? I've tried a few of different things, none of which work.

On my page, I have a few embedded presentations which I initialize in a for loop. Then I try to detect slidechanged events with .on('slidechanged', ...). This correctly detects slide changes on each presentation, but then console.log(rev.getCurrentSlide()) outputs the current slide of the last presentation on the page (regardless of which presentation had a slidechanged event).

var elms = document.getElementsByClassName( 'reveal' );
for ( var i = 0; i < elms.length; i++ ) {
    var rev = new Reveal( elms[ i ], {
        // config options
    } );

    rev.initialize();
    
    rev.on( 'slidechanged', event => { 
        console.log(rev.getCurrentSlide());
    });
}

What am I doing wrong?

[hakimel]

You can fix this by changing var rev to let rev.

The error here is due to how hoisting works in JS. Your var definition inside the for loop is hoisted to the scope/function where the for loop runs. This means your event listener is always referring to the same rev variable.

Using let or const makes it work because those variable types are only hoisted to the top of the current block (the for loop in this case).