I am trying to write a regex test in JavaScript to check if a string solely contains balanced single braces, solely containing balanced double braces should return false.

For example:

• if the string is "{something}", "abc{something}cbd", it should return true,

• if the string is "{something}abc{{somethingElse}}", "{{somethingElse}}{something}", it should also return true,

• however, if the string is "{{something}}" or "{{something}}abc{{somethingElse}}", it should return false

I have a regex solution for this, which is /(?<!{\s?){(?!\s?{)[^{}]+(?<!}\s?)}(?!\s?})/gm, however ios safari doesn't support negative lookbehind.