A syntactically ill-formed regular expression may be interpreted differently on different platforms and may even lead to a runtime error.

Examine the regular expression to see whether it contains any typos and correct them.

In the following example, the regular expression p{ is not well-formed: { begins a range quantifier of the form {n,m} specifying that the previous character is repeated between n and m times, but here it is not followed by anything. Most browsers will interpret this pattern as matching the literal string "p{", but this is not guaranteed by the ECMAScript standard.

To ensure portability, the opening curly brace should be escaped like this: /p\{/.

Mozilla Developer Network: JavaScript Regular Expressions.