Canvas reference: The closePath function

The closePath function designates a path as closed and (possibly) draws a connecting line back to the start point

The closePath function is used to mark the path you're drawing as closed so that you can begin another. It's important to remember that this function doesn't always need to be used - the deciding factor can be whether you want to draw a line back to the start point for the current path. Sometimes this isn't applicable though - such as when your path is only drawing a rectangle. In this case the closePath might not be needed and you can just start a new path with the beginPath function - and not call closePath. In this case the closePath is implied by starting a new path (but without drawing a connecting line to the start of the new path).

An example

<script>
    window.onload = function ()
    {
        var canvas  = document.getElementById("cvs");
        var context = canvas.getContext('2d');

        context.beginPath();
        context.arc(100,100, 50, 0, Math.PI, false);
        
        // This connects back to the start of the arc
        context.closePath();
    
        context.stroke();
    }
</script>