const regex = /^\([^|)]+\|[^)]+\) *\+ ?| \+? *\([^|)]+\|[^)]+\)/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^\\([^|)]+\\|[^)]+\\) *\\+ ?| \\+? *\\([^|)]+\\|[^)]+\\)', 'gm')
const str = `y ~ 1 + a + (b | c) + (d^2) + e + (1 | f) + g
y~1+a+(b|c)+(d^2)+e+ (1|f)+g
(b | c) + y ~ 1 + a + (d^2) + e + (1 | f) + g
y ~ 1 + a + (d^2) + e + (1 | f) + g + (b | c)
(h|i) + y ~ 1 + a + (b | c) + (d^2) + e + (1 | f) + g +(j+k| m)`;
const subst = ``;
// 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