JSONP Callback Regex

Developer

Regular expression

/^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*$/

Pattern breakdown

Part	Meaning
`Anchor or context`	Use anchors when you need whole-string validation.
`Main token`	The core token sequence describes the accepted text shape.
`Character class`	Character classes limit which characters are valid.
`Quantifier`	Quantifiers control how many characters or groups are accepted.
`Flags`	Use language-specific flags such as i, m, or u only when needed.

Should match

callback_1

Should not match

alert(1)
not matching sample
callback_1 invalid
alert(1)callback_1

Test cases

Input	Expected	Why it matters
`callback_1`	Match	Representative valid input for this pattern.
`alert(1)`	No match	Common invalid or boundary input.
`(empty string)`	No match	Common invalid or boundary input.
`not matching sample`	No match	Common invalid or boundary input.
`callback_1 invalid`	No match	Common invalid or boundary input.
`alert(1)callback_1`	No match	Common invalid or boundary input.

JavaScript

const re = /^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*$/;
re.test(input);

Python

import re
bool(re.search(r"^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*$", text))

PHP

$ok = preg_match('/^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^[A-Za-z_$][\\w$]*(?:\\.[A-Za-z_$][\\w$]*)*$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*$`)
ok := re.MatchString(value)

Notes and production use

JSONP Callback regex is useful as a practical starting point. Test it against your real input, avoid using it as the only security control, and prefer a parser when the format has complex grammar.

Performance tip: avoid running complex regular expressions repeatedly on very large untrusted strings without limits. Prefer anchored validation patterns, cap input length before matching, and use a parser when the target format has nested grammar.

JSONP Callback