Shooting Exercise

Trying to get shooting to work properly

HTML

<body>
        <!--Game Res-->
        <img id="alienW"            src="http://i.imgur.com/JsICPiM.png"/>
        <img id="alienB"            src="http://i.imgur.com/lAZKLpc.png"/>
        <img id="alienR"            src="http://i.imgur.com/k9B3guu.png"/>
        <img id="shot"              src="http://i.imgur.com/MxYI25K.png"/>
        <img id="player"            src="http://i.imgur.com/x59FP55.png"/>
        <imd id="player_explode"    src="http://i.imgur.com/iMTkTfj.png"/>
        <img id="dead_alien"        src="http://i.imgur.com/BIi4AXe.png"/>
        <img id="missile"           scr="http://i.imgur.com/alTQPXw.png"/>
        <img id="missile_wave"      src="http://i.imgur.com/6UNQBWv.png"/>
    <div>
        <canvas id="canvas">This text is displayed if your browser does not support HTML5 Canvas.</canvas>
        <script type='text/javascript' src='script.js'></script>
    </div>
</body>

CSS

/* Add your CSS below! */
div {
    margin:auto;
    width:400px;
    height:400px;
    border:1px dotted black;
    background-color:black;
}

canvas {
    margin:auto;
    width:400px;
    height:400px;
    border:1px dotted black;
    background-color:black;
}

img {
    display:none;
}

JavaScript

// Add your JavaScript below!
var canvas = document.getElementById("canvas");
var board = canvas.getContext("2d");
//Directional Shortcuts
var Right = 1;
var Left = 2;
var Up = 3;
var Down = 4;
//Edges
var LeftEdge = 0;
var RightEdge = canvas.width - 10;
var BottomEdge = canvas.height - 10;
//All alien array
var aliens = [];
//KeyCodes
var LeftArrow = 37;
var RightArrow = 39;
var UpArrow = 38;
var AKey = 65;
var DKey = 68;
var Spacebar = 32;
//Player/Shot variable
var shooting;

//Aliens
var moveAlien = function(alien){
    board.fillStyle = "black";
    board.fillRect(alien.x - 1, alien.y - 1, alien.img.width + 2, alien.img.height + 2);
    if(alien.state == Right && alien.x >= RightEdge){
        for(var i  = 0; i < aliens.length; i++){
            moveAlienDown(aliens[i]);
            aliens[i].state = Left;
        }
    }else if(alien.state == Left && alien.x <= LeftEdge){
        for(var j  = 0; j < aliens.length; j++){
            moveAlienDown(aliens[j]);
            aliens[j].state = Right;
        }
    }
    alien.setMoveDirection();
    board.drawImage(alien.img, alien.x, alien.y);
};

var moveAlienDown = function(alien){
    for(var i = 0;i < 10;i++){
        board.fillStyle = "black";
        board.fillRect(alien.x - 1, alien.y - 1, alien.img.width + 2, alien.img.height + 2);
        alien.y += 1;
        board.drawImage(alien.img, alien.x, alien.y);
    }
};

function Alien(x, y, scoreVar, pic){
    this.x = x;
    this.y = y;
    this.scoreVar = scoreVar;
    this.img = document.getElementById(pic);
    board.drawImage(this.img, this.x, this.y);
    this.path;
    this.moveDown;
    this.state;
    aliens.push(this);
    this.setMoveDirection = function(){
        switch(this.state){
            case Right:
                this.x += 1;
                break;
            case Left:
                this.x -= 1;
                break;
            case Up:
                this.y -= 1;
                break;
            case Down:
               ...