go to top 的箭頭語法

<!-- Scroll to Top -->

<script type="text/JavaScript">
var topMargin = 300
var slideTime = 1200
var ns6 = (!document.all && document.getElementById);
var ie4 = (document.all);
var ns4 = (document.layers);
window.setInterval("main()", 10)

function floatObject() {
if (ns4 || ns6) {
findHt = window.innerHeight;
} else if(ie4) {
findHt = document.body.clientHeight;
}
}

function main() {
if (ns4) {
this.currentY = document.floatLayer.top;
this.scrollTop = window.pageYOffset;
mainTrigger();
} else if(ns6) {
this.currentY = parseInt(document.getElementById('floatLayer').style.top);
this.scrollTop = scrollY;
mainTrigger();
} else if(ie4) {
this.currentY = floatLayer.style.pixelTop;
this.scrollTop = document.body.scrollTop;
mainTrigger();
}

}
function mainTrigger() {
var newTargetY = this.scrollTop + this.topMargin
if ( this.currentY != newTargetY ) {
if ( newTargetY != this.targetY ) {
this.targetY = newTargetY
floatStart();
}
animator();
}


}
function floatStart() {
var now = new Date()
this.A = this.targetY - this.currentY
this.B = Math.PI / ( 2 * this.slideTime )
this.C = now.getTime()
if (Math.abs(this.A) > this.findHt) {
this.D = this.A > 0 ? this.targetY - this.findHt : this.targetY + this.findHt
this.A = this.A > 0 ? this.findHt : -this.findHt
} else {
this.D = this.currentY
}
}
function animator() {
var now = new Date()
var newY = this.A * Math.sin( this.B * ( now.getTime() - this.C ) ) + this.D
newY = Math.round(newY)
if (( this.A > 0 && newY > this.currentY ) || ( this.A < 0 && newY < this.currentY )) {
if ( ie4 )floatLayer.style.pixelTop = newY
if ( ns4 )document.floatLayer.top = newY
if ( ns6 )document.getElementById('floatLayer').style.top = newY + "px"
}
}
//-->
</script>
<div id="floatLayer" style="position: absolute; height:20px; width:15; right:5px; top:400px; z-index: 100"><a href="#"><img vspace="0" border="0" hspace="0" alt="Back to Top" src="https://www.weebly.com/editor/uploads/7/6/7/0/76706939/custom_themes/349258210169178405/files/images/up-arrow.png" title="Back To Top Of Page" /></a></div><script type="text/javascript">