const regex = /\\(ref){eq:(.*?)}/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('\\\\(ref){eq:(.*?)}', 'gm')
const str = `\\ref{eq:0And1Qubit} hjhg
\\ref{eq:EulerForm}the state is measured, as it can be shown \$|\\rho e^{i\\theta}|^2=\\rho^2\$ (\$i\$ is always the imaginary unit in this report). In other words, it is not possible to measure the global phase. The description of \$\\ket{q}\$ can then be confined to \$\\alpha,\\beta,\\phi\\in\\mathbb{R}\$, where \$\\phi\$ is the relative phase \$\\phi=\\theta_\\beta-\\theta_\\alpha\$.`;
const subst = `\\eqref{eq:$2}`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions