我如何为我的这个javascript程序创建检测?

我一直在构建我们在课堂上做过的作业，我在检测部分被难住了。

我希望当我的new站在pokeball上时被"抓住"，玩家移动键盘来控制new, pokeball会在一段时间内随机重新定位。

我如何创建一个函数，将检测当新的gif与pokeball重叠?

var _stage = document.getElementById("stage");
var _Mew = document.querySelector("img");
var _PokeBall = document.getElementById("PokeBall");
_stage.style.width = "800px";
_stage.style.height = "600px";
_stage.style.backgroundColor = "black";
_stage.style.marginLeft = "auto";
_stage.style.marginRight = "auto";
_Mew.style.position = "relative"; // Uses top and left from parent
_PokeBall.style.position = "relative"; // Uses top and left from parent
var leftPressed = false;
var rightPressed = false;
var upPressed = false;
var downPressed = false;
var player = [ 400, 300 ]; // Left, Top
var PokeBall = [100, 100];// Top, Left
var uIval = setInterval(update, 22.22); // 30fps update loop
var map = [];  // empty Map Array
window.addEventListener("keydown", onKeyDown);
window.addEventListener("keyup", onKeyUp);
var Pval= setInterval(MovePokeball, 2000);
function generateMap()
{
    for (var row = 0; row < 2; row++)
    {
        for(var col = 0; col <8; col++)
        {
        console.log("In row "+row);
        }
    }
}
/*map[row] = []; // Creating new array in specified row
                for (var col = 0; col <8; col++)
                    {
                    console.log("In row "+row+"doing col"+col);
                    }
*/
function onKeyDown(event)
{
    switch(event.keyCode)
    {
        case 37: // Left.
                if ( leftPressed == false )
                    leftPressed = true;
                break;
        case 39: // Right.
                if ( rightPressed == false )
                    rightPressed = true;
                break;
        case 38: // Up.
                if ( upPressed == false )
                    upPressed = true;
                break;
        case 40: // Down.
                if ( downPressed == false )
                downPressed = true;
                break;
        default:
                console.log("Unhandled key.");
                break;
    }
}
function onKeyUp(event)
{
    switch(event.keyCode)
    {
        case 37: // Left.
                leftPressed = false;
                break;
        case 39: // Right.
                rightPressed = false;
                break;
        case 38: // Up.
                upPressed = false;
                break;
        case 40: // Down.
                downPressed = false;
                break;
        default:
                console.log("Unhandled key.");
                break;
    }
}
function update() // Going to run 30fps
{
    movePlayer();
    // move enemies
    // collision check
    // animate sprites
    PlayerCaught();
    render();
}
function movePlayer()
{
    if ( leftPressed == true && player[0] >= _Mew.width/2)
            player[0] -= 10;
    if ( rightPressed == true && player[0] < 800 - _Mew.width/2)
        player[0] += 10;
    if ( upPressed == true && player[1] >= _Mew.height/2 )
        player[1] -= 10;
    if ( downPressed == true && player[1] < 600 - _Mew.width/2)
        player[1] += 10;
}

function render()
{
    _Mew.style.left = player[0]-_Mew.width/2+"px";
    _Mew.style.top = player[1]-_Mew.width/2+"px";

}

function PlayerCaught()
{
    if (_PokeBall [100,100] = player [100,100])
    window.alert("Mew Has Been Captured!")

}
function MovePokeball()
{
    _PokeBall.style.left= Math.floor(Math.random()*801)+"px";
    _PokeBall.style.top= Math.floor(Math.random()*601)+"px";
}