JSON.parse(undefined) – Why It Fails and How to Fix It

Local processing

undefined is a JavaScript value, not JSON text. The fix is usually to correct the value flow before parsing rather than trying to make undefined valid JSON.

Indent

9 chars · 1 line

Two-way sync · Edit either side and the other updates automatically.

Invalid JSONExpected a JSON value
Line 1Column 1Character 1Found “u”
undefined
The highlighted character is where JSON parsing stopped.

JSON runtime troubleshooting

Why JSON.parse(undefined) fails before JSON parsing can begin

JSON has null but no undefined literal. When missing application state reaches JSON.parse, the parser receives something outside the JSON grammar and fails immediately. This tool is free to use. No account or payment is required.

Last updated

Diagnose the problem

Why this happens

The bug is usually before JSON.parse

Changing parser options cannot make JavaScript undefined part of JSON. The useful question is why the caller expected text but received no value.

  • A property name changed but the old path is still parsed.
  • A storage key is missing.
  • Code runs before an asynchronous response has populated state.

Do not confuse missing input with undefined inside JSON text

JSON.parse(undefined) is an application-state problem. A payload such as {"value":undefined} is a different syntax problem because the invalid literal appears inside the text itself.

Resolve the issue

Fix it step by step

  1. Log or inspect the exact value and typeof result immediately before JSON.parse.
  2. Trace the missing property, storage key, or asynchronous result that produced undefined.
  3. Handle the missing state explicitly, then call JSON.parse only when valid JSON text exists.

Use the solving tool

Recommended solution

Run the focused checker with the failing payload to locate the parser error and inspect the nearby source before changing data.

Open JSON Error Checker

JSON.parse(undefined) example

The failing value is not JSON text. The corrected path guards the missing value before parsing.

Value reaching JSON.parse

undefined

Valid JSON text example

{"name":"Ada"}

Common questions

Frequently asked questions

Is undefined valid JSON?

No. JSON defines null but does not define JavaScript's undefined value.

Why does localStorage sometimes lead to this error?

Missing or transformed storage values can become undefined in application code before JSON.parse is called. Inspect the exact value returned by your wrapper.

Should I stringify undefined before parsing it?

No. Fix the data flow and only parse actual serialized JSON text.

Debugging a specific JSON issue? Browse JSON troubleshooting.