Aircraft war from scratch (II) simple development

Last time we set up a background picture to move from top to bottom on the stage , But because there is only one background picture , There will always be a moment when the background image will slide down , That is to say, our background maintains a short continuity , But not for a long time , So we have to solve this problem , We need to load two background pictures on the stage as soon as we open , Use the clock control to control the two pictures to move together , And judge the position of the two pictures relative to the stage in real time , When the first picture is finished, the second picture is on the top , At the end of the second chapter, the first picture is on the top
stay html Add two pictures to

<div id="stage">
			<div class="bg1"></div>
			<div class="bg2"></div>
		</div>

js

$(function(){
    
	// When writing code here, you can control all htmldom Node 
	//dom
	
	var stage=document.getElementById("stage"); // Get stage nodes 
	var bg1=stage.getElementsByClassName("bg1")[0];// Get a background picture 
	// console.log(bg1) // Check to see if... Is captured bg1
	var bg2=stage.getElementsByClassName("bg2")[0];// Get a background picture 
	var topval=-200;
	var topval2=-968;
	var k=0;
	// bg1.style.cssText="top: -30px;"
	var t1=setInterval(function(){
    
		k++;
		if(k==768){
    
			topval=-968;
			
			
		}else if(k==768*2){
    
			topval2-968;
			k=0;
		}
		// console.log("ddd")
		// console.log(bg1.style.cssText)
		// bg1.scrollTop=bg1.scrollTop+10;
		bg1.style.cssText="top: "+topval+"px";
		topval+=1;
		bg2.style.cssText="top: "+topval2+"px";
		topval2+=1;
		//topval++ The background moves down  
		
	},10);
	
	// t1.clearInterval(); // The clock stopped 
	
	
	//  Chapter II pictures 
	// var stage=document.getElementById("stage"); // Get stage nodes 
	
	// // console.log(bg1) // Check to see if... Is captured bg1
	
	// // bg1.style.cssText="top: -30px;"
	// var t1=setInterval(function(){
    
	// // console.log("ddd")
	// // console.log(bg1.style.cssText)
	// // bg1.scrollTop=bg1.scrollTop+10;
	// bg2.style.cssText="top: "+topval2+"px";
	// topval2+=1
	// //topval++ The background moves down  
		
	// },70);
	
	
});