Avoid? No. Just use them with double backslash in RegExp constructor.

Same for Javascript, but only if we use new RegExp(regString) constructor.
We must use \\d instead of \d. Or [0-9]. Or String.raw`\d`

Why this tagged as "Regular Expressions"?

(!?1) !== (?!1).
(!?1) mean "zero or one !" then "1". So regexp can be rewritten to /0*1/g
But this solutions works despite this mistake.

Still incorrect expected output for randomised test in JS version of kata sometimes when we have 0 koef in input.

For example,

Input +1za+5z-5azb+1za+8z-12z+8zab-2az-3baz
Expected output z+0abz
But should be z