jquery draggable, making a div not to go outside of the other div frame

i need a draggable div not to go outside of second div frame, so far i managed to make a "collision" basically returning true or false if draggable div is inside the frame of other div. So the thing now is that i cant get this to work, i was trying to get it to a x = 90(example) when it hits the frame and few more examples , but i just can't get this to work. The draggable div doesn't want to go back to position.

Here is a JSFiddle: https://jsfiddle.net/kojaa/x80wL1mj/2/

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="style.css">
    <title>Catch a ball</title>
</head>
<body>
    <div class="catcherMovableArea" id="catcherMovableArea">
        <div id="catcher" class="catcher"></div>
    </div>
    <script src="script.js"></script>
</body>
</html>

.catcherMovableArea {
    position: absolute;
    border: 1px solid black;
    width: 1900px;
    top: 90%;
    height: 50px;
}

.catcher {
    position: absolute;
    width: 250px;
    height: 30px;
    border-radius: 10px;
    background-color: black;
    top: 20%;
}


let catcher = $("#catcher");

$(document).mousemove(function(e) {
    catcher.position({
      my: "left-50% bottom+50%",
      of: e,
      collision: "fit"
    });

    let catcherOffset = $(catcher).offset();
    let CxPos = catcherOffset.left;
    let CyPos = catcherOffset.top;

    let catcherYInMovableArea, catcherXInMovableArea = true;

    while(!isCatcherYinMovableArea(CyPos)){
        catcherYInMovableArea = false;
        break;
    }

    while(!isCatcherXinMovableArea(CxPos)){
        catcherXInMovableArea = false;
        break;
    }
});

function isCatcherYinMovableArea(ypos){
    if(ypos < 849.5999755859375 || ypos > 870.5999755859375) {
        return false;
    } else {
        return true;
    }
}

function isCatcherXinMovableArea(xpos){
    if(xpos < 8 || xpos > 1655 ) {
        return false;
    } else {
        return true;
    }
}

Solution

By default, the collision option will prevent the element from being placed outside of the window. You want to prevent it from moving outside of a specific element.

To do this, use the within option to select which element should be used for containment.

Example:

let draggable = $("#draggable");

$(document).mousemove(function(e) {
    draggable.position({
      my: "left-50% bottom+50%",
      of: e,
      collision: "fit",
      within: "#container"
    });
});

#container { width: 200px; height: 100px; border-style: solid }
#draggable { width: 50px; height: 50px; background-color: black }

<script src="https://code.jquery.com/jquery-3.3.1.js"></script>
<script src="https://code.jquery.com/ui/1.12.0-rc.1/jquery-ui.js"></script>

<div id="container">
  <div id="draggable"></div>
</div>