ignore this

var Vertex = function(x, y, z) {
this.x = parseFloat(x);
this.y = parseFloat(y);
this.z = parseFloat(z);
};

var Vertex2D = function(x, y) {
this.x = parseFloat(x);
this.y = parseFloat(y);
};

var Cube = function(center, side) {
// Generate the vertices
var d = side / 2;

this.vertices = [
new Vertex(center.x - d, center.y - d, center.z + d),
new Vertex(center.x - d, center.y - d, center.z - d),
new Vertex(center.x + d, center.y - d, center.z - d),
new Vertex(center.x + d, center.y - d, center.z + d),
new Vertex(center.x + d, center.y + d, center.z + d),
new Vertex(center.x + d, center.y + d, center.z - d),
new Vertex(center.x - d, center.y + d, center.z - d),
new Vertex(center.x - d, center.y + d, center.z + d)
];

// Generate the faces
this.faces = [
[this.vertices[0], this.vertices[1], this.vertices[2], this.vertices[3]],
[this.vertices[3], this.vertices[2], this.vertices[5], this.vertices[4]],
[this.vertices[4], this.vertices[5], this.vertices[6], this.vertices[7]],
[this.vertices[7], this.vertices[6], this.vertices[1], this.vertices[0]],
[this.vertices[7], this.vertices[0], this.vertices[3], this.vertices[4]],
[this.vertices[1], this.vertices[6], this.vertices[5], this.vertices[2]]
];
};

function project(M) {
// Distance between the camera and the plane
var d = 200;
var r = d / M.y;

return new Vertex2D(r * M.x, r * M.z);
}

function render(objects, ctx, dx, dy) {
// Clear the previous frame
ctx.clearRect(0, 0, 2*dx, 2*dy);

// For each object
for (var i = 0, n_obj = objects.length; i < n_obj; ++i) {
// For each face
for (var j = 0, n_faces = objects[i].faces.length; j < n_faces; ++j) {
// Current face
var face = objects[i].faces[j];

// Draw the first vertex
var P = project(face[0]);
ctx.beginPath();
ctx.moveTo(P.x + dx, -P.y + dy);

// Draw the other vertices
for (var k = 1, n_vertices = face.length; k < n_vertices; ++k) {
P = project(face[k]);
ctx.lineTo(P.x + dx, -P.y + dy);
}

// Close the path and draw the face
ctx.closePath();
ctx.stroke();
ctx.fill();
}
}
}

(function() {
// Fix the canvas width and height
var canvas = document.getElementById('cnv');
canvas.width = canvas.offsetWidth;
canvas.height = canvas.offsetHeight;
var dx = canvas.width / 2;
var dy = canvas.height / 2;

// Objects style
var ctx = canvas.getContext('2d');
ctx.strokeStyle = 'rgba(0, 0, 0, 0.3)';
ctx.fillStyle = 'rgba(0, 150, 255, 0.3)';

// Create the cube
var cube_center = new Vertex(0, 11*dy/10, 0);
var cube = new Cube(cube_center, dy);
var objects = [cube];

// First render
render(objects, ctx, dx, dy);

// Events
var mousedown = false;
var mx = 0;
var my = 0;

canvas.addEventListener('mousedown', initMove);
document.addEventListener('mousemove', move);
document.addEventListener('mouseup', stopMove);

// Rotate a vertice
function rotate(M, center, theta, phi) {
// Rotation matrix coefficients
var ct = Math.cos(theta);
var st = Math.sin(theta);
var cp = Math.cos(phi);
var sp = Math.sin(phi);

// Rotation
var x = M.x - center.x;
var y = M.y - center.y;
var z = M.z - center.z;

M.x = ct * x - st * cp * y + st * sp * z + center.x;
M.y = st * x + ct * cp * y - ct * sp * z + center.y;
M.z = sp * y + cp * z + center.z;
}

// Initialize the movement
function initMove(evt) {
clearTimeout(autorotate_timeout);
mousedown = true;
mx = evt.clientX;
my = evt.clientY;
}

function move(evt) {
if (mousedown) {
var theta = (evt.clientX - mx) * Math.PI / 360;
var phi = (evt.clientY - my) * Math.PI / 180;

for (var i = 0; i < 8; ++i)
rotate(cube.vertices[i], cube_center, theta, phi);

mx = evt.clientX;
my = evt.clientY;

render(objects, ctx, dx, dy);
}
}

function stopMove() {
mousedown = false;
autorotate_timeout = setTimeout(autorotate, 2000);
}

function autorotate() {
for (var i = 0; i < 8; ++i)
rotate(cube.vertices[i], cube_center, -Math.PI / 720, Math.PI / 720);

render(objects, ctx, dx, dy);

autorotate_timeout = setTimeout(autorotate, 30);
}
autorotate_timeout = setTimeout(autorotate, 2000);
})();

What is this for? What what coding language?

It looks like JS that makes a cube spin around, but I'm not totally sure

It is

I am working on a 3d Simulation in Javascript 2d Canvas

Hard to ignore . . . no, actually easy to. Thank you for the warning. 

U can comment if you want, but its probably not interesting to you

??

Its Javascript

I want to learn JS too...But it's not in my computer book.And on Internet,i cannot find the site where i can learn JS for free...    somebody please help.

Try buying "Javascript for kids", by Nick Morgan. I learned all my basic JS from it