Structural analysis in JavaScript

The whole integration

No initialisation call, no API key, no network. You hand it model JSON and it hands back an envelope you branch on.

import { calculate_from_json } from "@ferscloud/fers-calculation-web";

// A 5 m cantilever, IPE 180 in S235, 1 kN down at the tip.
const res = JSON.parse(calculate_from_json(JSON.stringify(model)));

if (res.ok) {
  const dy = res.result.results.loadcases["End Load"]
    .displacement_nodes["2"].dy;
  console.log(`Tip deflection: ${(dy * 1000).toFixed(3)} mm`);
  // Tip deflection: -15.065 mm
  // Hand check: PL³/3EI_z = 1000·5³ / (3 · 210e9 · 13.17e-6) = 15.07 mm
} else {
  console.error(res.error.code, res.error.message);
}

The printed value is the real output for those inputs, and the comment is the closed-form check it agrees with. That habit is worth copying: solve a case you already know before trusting one you do not.

Why put the solver in the browser

The loop a web form cannot do

One solve is a calculator. A thousand solves is a search — and once each one is free and instant, sweeping a parameter stops being something you batch overnight and becomes something the page does while someone drags a slider.

import { calculate_from_json } from "@ferscloud/fers-calculation-web";

// Which of these sections keeps the span within its deflection limit?
const limit = span / 300;

for (const section of catalogue) {
  const res = JSON.parse(
    calculate_from_json(JSON.stringify(buildModel(span, section))),
  );
  if (!res.ok) continue;

  const sag = Math.abs(midspanDeflection(res.result));
  if (sag <= limit) {
    console.log(section.name, (sag * 1000).toFixed(1), "mm");
  }
}

// Runs entirely in the visitor's browser: no request per iteration,
// no rate limit, no per-solve cost.

The solver is synchronous and CPU-bound, so for anything substantial run it in a Web Worker and keep the UI thread free.

// solver.worker.ts — keep the UI thread free.
import { calculate_from_json } from "@ferscloud/fers-calculation-web";

self.onmessage = (e: MessageEvent<{ id: number; model: string }>) => {
  const out = calculate_from_json(e.data.model);
  self.postMessage({ id: e.data.id, out });
};

Where it runs

Two packages are published from the same engine with an identical API: @ferscloud/fers-calculation-web for anything behind a bundler, and @ferscloud/fers-calculation for Node. React, Vue, Svelte and plain JavaScript all consume it the same way, and generated TypeScript model types ship alongside.

This is not a demo build. The FERS web app, the 2D frame calculator and every beam calculator on this site run on the same package you would install — so you can see exactly what it does before adding a dependency.

What it costs

Free for models up to 100 members, with no account and no key — that covers most beams, portal frames and small trusses. A short-lived signed token from your server raises the ceiling to 10,000 members. There is no per-solve charge in either case, because there is no server doing the solving.

Not building a front end?

• Structural analysis in Python — the same engine from a script, for anything repetitive or version-controlled.
• REST API — plain HTTP from any language, with an OpenAPI 3.1 spec.
• MCP server — let Claude, ChatGPT, Cursor or VS Code build and check models directly.