Assignment operator returning NaN

Question

I'm trying to keep track of the time while using window.requestAnimationFrame() but the += operator keeps returning NaN even though the value I'm incrementing by isn't NaN

var elapsedTime = 0
var lastTime = 0
var between = 500
var count = 0
var betweenCount = 0
function frame(time) {
    elapsedTime = time - lastTime
    console.log(elapsedTime)
    lastTime = time
    betweenCount += elapsedTime
    console.log(betweenCount)
    window.requestAnimationFrame(frame)
}

frame()

betweenCount should be keeping track of the total elapsed time since its last reset, but it becomes NaN as soon as elapsedTime is assigned to it, but elapsed time isn't NaN at that point.

Answer 1

Since you're calling frame() without any arguments the first time, time will be undefined in the function, elapsedTime will become undefined - lastTime which is NaN.

You need to give the initial frame() call a valid argument, e.g. 0.