通过闭包和setTimeout让背景颜色从黄变白再变紫红

var b = document.body.style

function changeColor (s,interval){

s.backgroundColor = '#ffffcc'

var level = 2

var changepoint = false

var step = function(){

if(level === -1 && changepoint){

return;
}

var hex  = level.toString(16)

if(changepoint){

//console.log('now change')

s.backgroundColor = '#ff' + hex + hex + 'ff'

}

else {

s.backgroundColor = '#ffff' + hex + hex

}

if(level <16 && !changepoint) {

level ++

if(level === 16 ) {

changepoint = true
}
}

if(level >= 0 && changepoint){

level--
}

setTimeout(step,interval)

//console.log(level,changepoint)

}

setTimeout(step,interval)

}

changeColor(b,50)