attention attrapez-le il s'enfuit !!

<style>
    #hihi {
        background-color: cyan;
        color: blue;

        text-align: center;
        align-content: center;

        width: 100px;
        height: 100px;
        position: absolute;
        left: 0px;
        top: 0px;
    }
</style>
<br>
<a id="hihi" href="3.html">la suite !!!</a>

<script>
    const hihi = document.getElementById("hihi");

    let x = 300; y = 200; phi = 0;
    let t = 0; T = 0;
    let Tmin = 100; Tmax = 200;
    let speed = 15;

    function moveLoop(){
        if (t == T){
            phi = 2*Math.PI*Math.random(); // nouvel angle
            vx = Math.floor(speed * Math.cos(phi));
            vy = Math.floor(speed * Math.sin(phi));
            T = Math.floor(Tmin + (Tmax-Tmin)*Math.random()); // nouvelle durée de cycle
            t = 0;
            console.log('CHANGEMENT', phi, T)
        }

        if (t == 0){
            hihi.style.backgroundColor = "red"
        } else if (t > 1) {
            hihi.style.backgroundColor = "cyan"
        }
        
        if ((x<0 & vx<0) || (x>window.innerWidth-100 & vx>0)) {
            phi = (phi < Math.PI) ? Math.PI - phi : 3*Math.PI - phi; // π-phi % 2π
            vx = Math.floor(speed * Math.cos(phi));
            vy = Math.floor(speed * Math.sin(phi)); // inchangé en pratique
            console.log('boumx', phi)
            hihi.style.backgroundColor = "yellow"
        }
        if ((y<0 & vy<0) || (y>window.innerHeight-100 & vy>0)) {
            phi = 2*Math.PI - phi; // -phi % 2π
            vx = Math.floor(speed * Math.cos(phi)); // inchangé en pratique
            vy = Math.floor(speed * Math.sin(phi));
            console.log('boumy', phi)
            hihi.style.backgroundColor = "yellow"
        }

        x += vx;
        y += vy;
        hihi.style.transform = `translate(${x}px, ${y}px)`;
        // plus rapide que hihi.style.left hihi.style.top

        t++;
    };
        
    setInterval(moveLoop, 30);

    /*
    // https://stackoverflow.com/questions/4467539/javascript-modulo-gives-a-negative-result-for-negative-numbers/17323608#17323608
    function mod(n, m) {
        return ((n % m) + m) % m;
    }
    */
</script>