Question

So, I am seeing a curious problem. If I have a function

// counter wraps around to beginning eventually, omitted for clarity. var counter;  cycleCharts(chartId) {     // chartId should be undefined when called from setInterval     console.log('chartId: ' + chartId);     if(typeof chartId == 'undefined' || chartId < 0) {         next = counter++;     }     else {         next = chartId;     }     // ... do stuff to display the next chart } 

This function can be called explicitly by user action, in which case chartId is passed in as an argument, and the selected chart is shown; or it can be in autoplay mode, in which case it’s called by a setInterval which is initialized by the following:

var cycleId = setInterval(cycleCharts, 10000); 

The odd thing is, I’m actually seeing the cycleCharts() get a chartId argument even when it’s called from setInterval! The setInterval doesn’t even have any parameters to pass along to the cycleCharts function, so I’m very baffled as to why chartId is not undefined when cycleCharts is called from the setInterval.

Answer 1

setInterval is feeding cycleCharts actual timing data ( so one can work out the actual time it ran and use to produce a less stilted response, mostly practical in animation )

you want

 var cycleId = setInterval(function(){ cycleCharts(); }, 10000);  

( this behavior may not be standardized, so don’t rely on it too heavily )