Examples
Positive lookbehind assertion
Text preceding the current location must match the assertion
const RE_DOLLAR_PREFIX = /(?<=\$)foo/g;
console.log("$foo %foo foo".replace(RE_DOLLAR_PREFIX, "bar")); // '$bar %foo foo'Negative lookbehind assertion
Text preceding the current location must not match the assertion
const RE_NO_DOLLAR_PREFIX = /(?<!\$)foo/g;
console.log("$foo %foo foo".replace(RE_NO_DOLLAR_PREFIX, "bar")); // '$foo %bar bar'