CS4 Code not working in movieclip

[Vadersapien]

Hello,
I can place the following code on a movieclip:

onClipEvent(load) {
    gravity = 0.2;
    yspeed = 0;
    speed = 2;
}
onClipEvent(enterFrame) {
    if(flipped) {
        this._xscale = -this._xscale;
        flipped = false;
    }
    if(this._x >= 763 or this._x <= 37) {
        flipped = true;
        speed = -speed;
    }
    if(!_parent.bricks.hitTest(_x+_width/2, _y+_height/4, true)) {
        _x += speed;
    }
    yspeed += gravity;
    while(_parent.bricks.hitTest(_x, _y+_height/2, true)) {
        _y--;
        yspeed = 0;
        jumping = 0;
    }
    if((!_parent.bricks.hitTest(_x, _y+_height/2+1, true)) or (yspeed<0)) {
        _y += yspeed;
    } else {
        yspeed = 0;
        jumping = 0;
    }
} 

And it'll work fine, however if I place it like this on a frame in the movieclip:

this.onLoad = function() {
    gravity = 0.2;
    yspeed = 0;
    speed = 2;
}
this.onEnterFrame = function() {
    if(flipped) {
        this._xscale = -this._xscale;
        flipped = false;
    }
    if(this._x >= 763 or this._x <= 37) {
        flipped = true;
        speed = -speed;
    }
    if(!_parent.bricks.hitTest(_x+_width/2, _y+_height/4, true)) {
        _x += speed;
    }
    yspeed += gravity;
    while(_parent.bricks.hitTest(_x, _y+_height/2, true)) {
        _y--;
        yspeed = 0;
        jumping = 0;
    }
    if((!_parent.bricks.hitTest(_x, _y+_height/2+1, true)) or (yspeed<0)) {
        _y += yspeed;
    } else {
        yspeed = 0;
        jumping = 0;
    }
} 

It doesn't work

Any help would be greatly appreciated since this is for a school project due in a week...