Physics check on individiual objects.

[Juice]

In my game I have a player, and I have several collision boxes, I want to know how to run a collision check on the box i'm closest to, or how to run them individually.

 

My code:

var player = {	x:32,	y:32,	size:32,	grav:0,	xspeed:0,	terminalVel:10,	onGround:false,	friction:0.8,	update:function() {		if (this.onGround == true) {			this.grav = 0;		} else if (this.onGround == false) {			this.grav += 0.4;		}		if (this.xspeed > this.terminalVel) {			this.xpseed = this.terminalVel;		}		if (this.grav > this.terminalVel) {			this.grav = this.terminalVel;		}		this.xspeed *= this.friction;		this.x += this.xspeed;		this.y += this.grav;		// Collision		for (var key in boxes) {			// Vertical			if ((this.y+this.grav >= boxes[key].y-32 && this.y <= boxes[key].y) && (this.x <= boxes[key].x+boxes[key].width)) {				this.onGround = true;				this.y = boxes[key].y-32;			} else {				this.onGround = false;			}		}	}};function basicBox(x,y,width,height,color) {	this.color = color;	this.x = x;	this.y = y;	this.width = width;	this.height = height;	this.draw = function() {		g.fillStyle = this.color;		g.fillRect(this.x,this.y,this.width,this.height);	}}var boxes = [	new basicBox(32,128,32,32,"blue"),	new basicBox(64,256,32,64,"orange"),	new basicBox(256,32,128,64,"red"),];function run() { // game loop    for (var key in boxes) {        boxes[key].draw();    }    player.update();}

I am pretty new to javascript, so how would I go about doing this?