evanw/esbuild · error · LexerPanic

Invalid binding pattern

Error message

Invalid binding pattern

What it means

Once esbuild decides a parenthesized expression is an arrow function, it validates the parameter bindings. If the collected binding tokens were not legal bindings (invalidLog.invalidTokens is non-empty), it logs 'Invalid binding pattern' for each offending token and aborts.

Source

Thrown at internal/js_parser/js_parser.go:3304

			}
		}

		// Arrow function parsing may be forced if this parenthesized expression
		// was prefixed by a TypeScript type parameter list such as "<T,>()"
		if isArrowFn || opts.forceArrowFn {
			if commaAfterSpread.Start != 0 {
				p.log.AddError(&p.tracker, logger.Range{Loc: commaAfterSpread, Len: 1}, "Unexpected \",\" after rest pattern")
			}
			p.logArrowArgErrors(&arrowArgErrors)
			p.logDeferredArrowArgErrors(&errors)

			// Now that we've decided we're an arrow function, report binding pattern
			// conversion errors
			if len(invalidLog.invalidTokens) > 0 {
				for _, token := range invalidLog.invalidTokens {
					p.log.AddError(&p.tracker, token, "Invalid binding pattern")
				}
				panic(js_lexer.LexerPanic{})
			}

			// Also report syntax features used in bindings
			for _, entry := range invalidLog.syntaxFeatures {
				p.markSyntaxFeature(entry.feature, entry.token)
			}

			arrow := p.parseArrowBody(args, fnOrArrowDataParse{
				needsAsyncLoc: loc,
				await:         await,
			})
			arrow.IsAsync = isAsync
			arrow.HasRestArg = spreadRange.Len > 0
			p.popScope()
			return js_ast.Expr{Loc: loc, Data: arrow}
		}
	}

View on GitHub (pinned to f6058f8364)

Solutions

1. Correct the destructuring pattern to use valid property names and commas.
2. Remove stray tokens/operators from the parameter list.
3. If the code is TypeScript, ensure the .ts/.tsx loader is used so types parse.

Example fix

// before
const f = ({a-b}) => a
// after
const f = ({a, b}) => a

import "github.com/evanw/esbuild/pkg/api"
res := api.Transform(src, api.TransformOptions{Loader: api.LoaderTS})
for _, m := range res.Errors {
  if strings.Contains(m.Text, "Invalid binding pattern") {
    // m.Location is the bad token in the arrow parameter list
  }
}

When it happens

Trigger: Arrow parameters that are not valid destructuring/identifier bindings, e.g. '({a-b}) => {}', '(123) => {}', or a stray ':'/operator inside the parameter list.

Common situations: Malformed destructuring in arrow params; leftover TypeScript annotation parsed as JS (wrong loader); partial edits leaving stray tokens.

Related errors

• Unexpected newline before "=>"
• Unexpected ":"
• Unexpected "..."
• Unexpected "," after rest pattern
• For loop initializers cannot start with "async of"

AI-assisted analysis of evanw/esbuild@f6058f8364 (2026-08-09). Data as JSON: /api/errors/43345eee88f6430b. Report an issue: GitHub.