Ich habe den folgenden Code am erstelltjsfiddle. Das Ziel ist es, ein Kästchen vom Canvas zu entfernen, nachdem es angeklickt wurde. Was tatsächlich passiert, ist, dass das Gitter gelöscht und komplett neu gezeichnet wird, während sich das entfernte Kästchen an der alten Stelle befindet. Das Gitter erscheint erst dann leer, wenn alle angegebenen Objekte entfernt wurden ... Ich bin verwirrt! Was mache ich falsch?

jQuery(function(){

    GridBox = new GridBox();

    GridBox.init();

    var canvas    = GridBox.canvas;

    canvas.on( 'click', GridBox.clickHandler );

});

function GridBox()
{

    this.target        = { x: 0, y: 0 };
    this.current       = { x: 0, y: 0 };
    this.boxHeight     = 50;
    this.boxWidth      = 50;
    this.width         = 500;
    this.height        = 500;
    this.context       = null;
    this.canvas        = null;

    var self = this,
        init = false,
        bw   = this.width,
        bh   = this.height,
        p    = 0,
        cw   = bw + ( p * 2 ) + 1,
        ch   = bh + ( p * 2 ) + 1;

    /**
     * Array of boxes that are painted on the grid.
     * Each box has its own x and y coordinates.
     */
    this.boxesOnGrid    = [
        { x: 2, y: 2 },
        { x: 9, y: 2 },
        { x: 5, y: 5 }
    ];

    /**
     * Initiate this object
     * @constructor 
     */
    this.init    = function()
    {
        if( !init ) {
            var canvas    = jQuery( '<canvas/>' ).attr({ width: cw, height: ch }).appendTo( 'body' );

            this.canvas     = canvas;
            this.context    = this.canvas.get( 0 ).getContext( '2d' );

            this.createGrid();

            init    = true;

        }
    };

    this.clearGrid        = function()
    {
        alert( 'clearing grid' );
        this.context.clearRect( 0, 0, 500, 500 );
    };

    /**
     * Create the grid 
     */
    this.createGrid        = function()
    {
        for( var x = 0; x <= bw; x += this.boxWidth ) {
            this.context.moveTo( 0.5 + x + p, p );
            this.context.lineTo( 0.5 + x + p, bh + p );
        }

        for( var x = 0; x <= bh; x += this.boxHeight ) {
            this.context.moveTo( p, 0.5 + x + p );
            this.context.lineTo( bw + p, 0.5 + x + p );
        }

        this.context.strokeStyle    = "#aaa";
        this.context.stroke();

        var boxes    = this.boxesOnGrid;

        this.boxesOnGrid    = [];

        for( key in boxes ) {
            var currentBox    = boxes[ key ];
            alert( 'i want to create box ' + currentBox.x + 'x' + currentBox.y );
            this.createBoxAt( currentBox.x, currentBox.y );
        }
    };

    /**
     * Find a suitable path between two boxes
     */
    this.findPath        = function()
    {

    };

    this.clickHandler    = function( event )
    {
        var clickOffset        = {
                x:    event.offsetX,
                y:    event.offsetY
            }, clickedBox    = {
                x:    Math.ceil( clickOffset.x / 50 ),
                y:    Math.ceil( clickOffset.y / 50 )
            };

        for( key in GridBox.boxesOnGrid ) {
            if( GridBox.boxesOnGrid[ key ].x === clickedBox.x && GridBox.boxesOnGrid[ key ].y === clickedBox.y ) {
                GridBox.clearGrid();
                GridBox.removeBox( key );
                GridBox.createGrid();
            }
        }

    };

    /**
     * Remove a box from the grid by removing it from the boxes array
     * and re-drawing the grid.
     */
    this.removeBox        = function( key )
    {
        alert( 'removing box ' + key );
        this.boxesOnGrid.splice( key, 1 );
    };

    /**
     * Create a box at a given coordinate on the grid
     * @param    {int} x
     * @param    {int} y 
     */
    this.createBoxAt    = function( x, y )
    {
        var box    = {
                x:    x * this.boxWidth - this.boxWidth,
                y:    y * this.boxHeight - this.boxHeight
            };

        this.createBox( box.x, box.y );
        this.saveBox( x, y );
    };

    this.createBox    = function( xpos, ypos )
    {
        this.context.rect( xpos, ypos, this.boxWidth, this.boxHeight );
        this.context.fillStyle    = '#444';
        this.context.fill();
    };

    this.saveBox    = function( x, y )
    {
        this.boxesOnGrid.push( { x: x, y: y } );
    };
}​