Constant SCRIPT 

pub const SCRIPT: &str = r#"(()=>{"use strict";const w=window,d=document,n=navigator,E="/_rws/t";if(n.webdriver&&!w.rwsTrackAutomation)return;
let p=location.pathname+location.search,s=Date.now(),m=0,on=d.visibilityState!=="hidden",shown=on?s:0,acc=0;
const send=b=>{const t=JSON.stringify(b);try{if(n.sendBeacon&&n.sendBeacon(E,t))return}catch(e){}try{fetch(E,{method:"POST",body:t,keepalive:true,credentials:"omit"})}catch(e){}};
const depth=()=>{const h=d.documentElement,y=(w.scrollY||0)+w.innerHeight;m=Math.max(m,Math.min(1,y/Math.max(h.scrollHeight,1)))};
const seen=()=>acc+(on?Date.now()-shown:0);
const leave=()=>{if(!p)return;depth();send({t:"leave",p,ms:seen(),sd:Math.round(m*100),w:w.innerWidth||0});p=null};
const start=np=>{p=np;s=Date.now();m=0;acc=0;shown=s};
addEventListener("scroll",depth,{passive:true});
d.addEventListener("visibilitychange",()=>{if(d.visibilityState==="hidden"){if(on){acc+=Date.now()-shown;on=false}leave()}else{if(!p)start(location.pathname+location.search);on=true;shown=Date.now()}});
addEventListener("pagehide",leave);
const nav=()=>{const np=location.pathname+location.search;if(np===p)return;const from=p;leave();start(np);send({t:"view",p:np,r:from})};
for(const k of["pushState","replaceState"]){const o=history[k];history[k]=function(){const r=o.apply(this,arguments);nav();return r}}
addEventListener("popstate",nav);
w.rws=w.rws||{};w.rws.track=(name,props)=>{const q={};if(props&&typeof props==="object")for(const k of Object.keys(props).slice(0,4))q[String(k).slice(0,32)]=String(props[k]).slice(0,64);send({t:"event",p:location.pathname+location.search,n:String(name).slice(0,64),q})};
depth()})();
"#;

The script. No dependencies, no storage, ~1.6 KB (0.8 KB compressed). The first page view is already counted by the server, so it reports only what happens after: leaving a page (time, scroll, width), route changes, events.