Text Processingflags: gm

JavaScript Variable Declaration

Match JavaScript / TypeScript variable declarations (`var`, `let`, `const`), capturing the keyword and identifier name.

Available in

JavaScript / ECMAScript code

jsJavaScript

const re = new RegExp("\\b(var|let|const)\\s+([a-zA-Z_$][\\w$]*)\\s*(?:=|;|$)", "gm");
const input = "const x = 1;\\nlet name = \"alice\";\\nvar count;";
const matches = [...input.matchAll(re)];
console.log(matches.map(m => m[0]));

Uses `String.prototype.matchAll` for global iteration (Node 12+ / all modern browsers).

Python (re) code

pyPython

import re

pattern = re.compile(r"\b(var|let|const)\s+([a-zA-Z_$][\w$]*)\s*(?:=|;|$)", re.MULTILINE)
input_text = "const x = 1;\\nlet name = \"alice\";\\nvar count;"
for m in pattern.finditer(input_text):
    print(m.group(0))

Stdlib `re` module — no third-party dependency. Works on Python 3.6+.

Go (RE2) code

goGo

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`(?m)\b(var|let|const)\s+([a-zA-Z_$][\w$]*)\s*(?:=|;|$)`)
	input := `const x = 1;\nlet name = "alice";\nvar count;`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}

Uses `regexp.MustCompile` (panics on bad patterns at startup) and `FindAllString` for all matches.

Pattern

regexengine-agnostic

\b(var|let|const)\s+([a-zA-Z_$][\w$]*)\s*(?:=|;|$)   (flags: gm)

Raw source: \b(var|let|const)\s+([a-zA-Z_$][\w$]*)\s*(?:=|;|$)

How it works

\b(var|let|const) captures the declaration keyword at a word boundary. \s+ requires whitespace. ([a-zA-Z_$][\w$]*) captures a valid JS identifier (starts with letter, underscore, or $). \s*(?:=|;|$) matches the assignment or terminator so we don't mis-match function parameters.