If you use NPM
npm install mathml-to-latex --save
If you use Yarn
yarn add mathml-to-latex
const Mathml2latex = require('mathml-to-latex');
const mathml = `
<math>
<mrow>
<mn>a</mn>
<mo>+</mo>
<mn>b</mn>
</mrow>
</math>
`;
Mathml2latex.convert(mathml);
// => a + b
const Mathml2latex = require('mathml-to-latex');
const mathml = `
<math>
<mrow>
<mi>A</mi>
<mo>=</mo>
<mfenced open = "[" close="]">
<mtable>
<mtr>
<mtd><mi>x</mi></mtd>
<mtd><mi>y</mi></mtd>
</mtr>
<mtr>
<mtd><mi>z</mi></mtd>
<mtd><mi>w</mi></mtd>
</mtr>
</mtable>
</mfenced>
</mrow>
</math>
`;
Mathml2latex.convert(mathml);
// => A = \begin{bmatrix} x & y \\ z & w \end{bmatrix}