factor-js

Factor analysis (principal factor analysis) and SVD in pure JavaScript and WebAssembly.

Given a table of observations, factor() reduces correlated variables to a handful of latent factors, tells you how much variance each one explains, and gives you per-row factor scores you can feed into downstream models. svd() exposes the underlying singular value decomposition if you want it directly.

• Runs in Node, Bun and the browser, with ESM, CommonJS and a UMD global build.
• Ships bundled TypeScript types.
• Optional WASM backend (AssemblyScript) for browser/Bun workloads.
• Results match the Python references (factor-analyzer, NumPy) and the SVD from pca-js.

Install

npm install factor-js     # or: bun add factor-js

Quickstart

Node / Bun (ESM)

import { factor, svd } from "factor-js";

Node (CommonJS)

const { factor, svd } = require("factor-js");

Browser (ESM, via jsDelivr)

<script type="module">
  import { factor } from "https://cdn.jsdelivr.net/npm/factor-js@1.0.4/+esm";
</script>

Browser (global)

<script src="https://cdn.jsdelivr.net/npm/factor-js@1.0.4/dist/factor.js"></script>
<script>
  // window.Factor.factor(...), window.Factor.svd(...)
</script>

WASM (ESM only; faster in Bun and browsers — see the benchmark below)

import { factor } from "factor-js/wasm";

A worked example, with actual results

The repo bundles a real dataset: tests/data.csv, 405 responses × 40 self-report variables (mood, body, senses, cognition, social feelings), each rated on a −3…3 scale. Rows are observations, columns are variables.

import { readFileSync } from "node:fs";
import { factor } from "factor-js";

const rows = readFileSync("tests/data.csv", "utf8").trim().split("\n");
const names = rows[0].split(",");
const data = rows.slice(1).map((r) => r.split(",").map(Number));

const { loadings, variance, scores } = factor(data);
const nVars = names.length;

// Eigenvalue = variance * number of variables (Kaiser criterion: keep eigenvalue > 1)
console.log("Factor  Explained  Eigenvalue  Cumulative");
let cumulative = 0;
variance.slice(0, 4).forEach((v, i) => {
  cumulative += v;
  console.log(
    `F${i + 1}`.padEnd(7),
    `${(v * 100).toFixed(2)}%`.padStart(9),
    (v * nVars).toFixed(2).padStart(10),
    `${(cumulative * 100).toFixed(2)}%`.padStart(11)
  );
});

// The variables with the strongest loading on each of the first three factors
for (let f = 0; f < 3; f++) {
  const top = names
    .map((name, i) => ({ name, loading: loadings[i][f] }))
    .sort((a, b) => Math.abs(b.loading) - Math.abs(a.loading))
    .slice(0, 6);
  console.log(`\nFactor ${f + 1}:`);
  top.forEach((t) => console.log(`  ${t.name.padEnd(14)} ${t.loading >= 0 ? "+" : ""}${t.loading.toFixed(3)}`));
}

That prints:

Factor  Explained  Eigenvalue  Cumulative
F1         41.99%      16.80      41.99%
F2         13.85%       5.54      55.84%
F3          9.32%       3.73      65.16%
F4          2.72%       1.09      67.88%

Factor 1:
  joy            +0.856
  happy          +0.851
  pleasure       +0.827
  love           +0.822
  angry          +0.811
  nauseated      +0.808

Factor 2:
  computations   +0.829
  recognizing    +0.798
  remembering    +0.722
  reasoning      +0.630
  hungry         -0.610
  communicating  +0.589

Factor 3:
  seeing         +0.638
  temperature    +0.607
  odors          +0.542
  sounds         +0.502
  embarrassed    -0.491
  guilt          -0.410

What the analysis actually says

• F1 explains ~42% on its own. 39 of the 40 variables load positively on it (joy and depressed together, happy and angry together). That is the classic signature of a general factor — a broad "rate-everything-high" response tendency rather than a positive-vs-negative mood axis. Always eyeball F1 before naming it.
• F2 (~14%) contrasts cognition against interoception. Mental/verbal items (computations, recognizing, remembering, reasoning) load positive, while bodily needs (hungry, pain) load negative.
• F3 (~9%) contrasts the exteroceptive senses against social emotion. Sight, temperature, smell and hearing load positive; embarrassed and guilt load negative.
• Four factors are worth keeping (Kaiser criterion: eigenvalue > 1 → variance × nVars > 1), together ~68% of the variance. The first ten reach ~78%.
• In practice: you can replace these 40 correlated items with ~4 composite scores per respondent for clustering, regression or embedding, losing a third of the (mostly noisy) variance.

The dataset is a demo fixture, not a validated psychometric instrument — treat the labels above as an example of reading the output, not a scientific claim.

Interpreting the return value

Field	Shape	Meaning
loadings	nVars × nFactors	Correlation of each variable with each factor
variance	nFactors	Share of total variance explained (sums to 1)
scores	nObs × nFactors	Per-observation factor scores

Eigenvalues are variance.map(v => v * nVars). Factor directions are sign-corrected so each factor's loadings sum to a positive value.

SVD directly

import { svd } from "factor-js";

// A is rows × columns, with rows >= columns
const A = [
  [1, 2],
  [3, 4],
  [5, 6],
];

const { U, S, V } = svd(A);
// A ≈ U · diag(S) · Vᵀ

JavaScript or WASM?

svd()/factor() do the same math in both builds, and produce bit-identical results (the test suite cross-checks them). Which is faster depends on the engine:

• Bun / JavaScriptCore / browsers: WASM is the better default, especially for the larger, more complex cases.
• Node / V8: V8's JIT is extremely good at warm numeric loops, and WASM starts to lose on large workloads. Both are fast; pick JS for simplicity.

Median time per call (lower is better; WASM/JS < 1× means WASM wins):

Bun 1.4.2 (Apple Silicon)

Test	Size	JS	WASM	WASM/JS
SVD	100×10	0.11ms	0.23ms	2.04×
SVD	1000×20	4.32ms	2.09ms	0.48×
SVD	1000×100	53.53ms	43.24ms	0.81×
Factor (real data)	405×40	6.03ms	4.66ms	0.77×
Factor (random)	1000×40	13.09ms	12.50ms	0.95×

Node 22 (V8, Apple Silicon)

Test	Size	JS	WASM	WASM/JS
SVD	100×10	1.76ms	0.28ms	0.16×
SVD	1000×20	2.17ms	4.80ms	2.21×
SVD	1000×100	54.43ms	104.44ms	1.92×
Factor (real data)	405×40	4.95ms	8.84ms	1.79×
Factor (random)	1000×40	13.23ms	22.78ms	1.72×

Reproduce with npm run bench under either node or bun. The WASM backend uses the AssemblyScript minimal runtime and flat row-major buffers; that is what closed most of the historical gap.

API

factor(data: number[][]): FactorResult

Principal factor analysis on a row-major matrix. Columns are standardised internally.

• data — observations × variables, rows >= columns.
• Returns { loadings, scores, variance } as above.
• Throws Need more rows than columns if rows < columns.

svd(A: number[][]): { U, S, V }

Singular value decomposition via A ≈ U · diag(S) · Vᵀ.

• A — rows × columns, rows >= columns.
• U is rows × columns, S has length columns, V is columns × columns.
• Throws Need more rows than columns if rows < columns.

factor() standardises its input first, so you do not need to center or scale data yourself. svd() operates on exactly the matrix you give it.

Building and testing

npm install
npm run build:all   # asc -> core/*.wasm, tsc + rollup -> dist/*
npm test            # JS-vs-WASM parity across random, edge and real-data cases
npm run bench       # JS-vs-WASM benchmark (run under node or bun)

The tests are generated with AI assistance and cross-check against NumPy and factor-analyzer. The Python side lives in python/:

python -m venv venv && source venv/bin/activate
pip install -r python/requirements.txt
python python/test_sample.py   # random sample
python python/test_data.py     # tests/data.csv

License

GPL-3.0-only. This work derives from pca-js.