# Node.js interface

:::{note}
See [Environment variables](../env.md) for the runtime environment variables.
:::

If [Node.js interface is installed](../install/install-nodejs.md), one can use the Node.js interface for model inference, which is a wrapper of [the header-only C++ API](./cxx.md).

A simple example is shown below.

```js
const deepmd = require("deepmd-kit");

const dp = new deepmd.DeepPot("graph.pb");

const coord = [1, 0, 0, 0, 0, 1.5, 1, 0, 3];
const atype = [1, 0, 1];
const cell = [10, 0, 0, 0, 10, 0, 0, 0, 10];

const v_coord = new deepmd.vectord(coord.length);
const v_atype = new deepmd.vectori(atype.length);
const v_cell = new deepmd.vectord(cell.length);
for (var i = 0; i < coord.length; i++) v_coord.set(i, coord[i]);
for (var i = 0; i < atype.length; i++) v_atype.set(i, atype[i]);
for (var i = 0; i < cell.length; i++) v_cell.set(i, cell[i]);

var energy = 0.0;
var v_forces = new deepmd.vectord();
var v_virials = new deepmd.vectord();

energy = dp.compute(energy, v_forces, v_virials, v_coord, v_atype, v_cell);

console.log("energy:", energy);
console.log(
    "forces:",
    [...Array(v_forces.size()).keys()].map((i) => v_forces.get(i)),
);
console.log(
    "virials:",
    [...Array(v_virials.size()).keys()].map((i) => v_virials.get(i)),
);
```

Energy, forces, and virials will be printed to the screen.
