JSON.parse Error in JavaScript: Common Causes and Fixes

Catch the error first

Wrap parsing in try/catch so you can inspect the bad payload and error message instead of crashing the app.

try {
  const data = JSON.parse(raw)
} catch (error) {
  console.error('Invalid JSON:', raw)
  console.error(error)
}

For the full safe parsing flow, see JSON.parse in JavaScript.

Trailing commas

// Invalid
{"name":"Alice",}

// Valid
{"name":"Alice"}

JavaScript object literals sometimes allow patterns that JSON does not. Trailing commas are a common example.

Single quotes instead of double quotes

// Invalid JSON
{'name':'Alice'}

// Valid JSON
{"name":"Alice"}

JSON strings and object keys must use double quotes. If the source looks like a JavaScript object literal, it may need cleanup before parsing.

Unquoted keys

// Invalid
{name:"Alice"}

// Valid
{"name":"Alice"}

Comments and invalid escape sequences

// Invalid JSON with comments
{
  // user name
  "name": "Alice"
}

// Invalid escape
{"path":"C:
ew	est"}

// Valid escaped backslashes
{"path":"C:\new\test"}

If you need a JSON-safe string literal, the patterns in JSON.stringify tutorial are useful.

Debug the exact broken character

When the error reports a position, log the surrounding slice of the string so you can see what is actually there.

try {
  JSON.parse(raw)
} catch (error) {
  const start = Math.max(0, 40)
  console.log(raw.slice(start, start + 120))
}

Prevent JSON.parse errors upstream

• Always generate JSON with JSON.stringify(), not by manual string concatenation.
• Validate pasted or uploaded JSON before storing it.
• Be careful when reading JSON from localStorage or query strings.
• Normalize nested payloads before logging or reusing them.

If your payload is deeply nested, parse nested JSON in JavaScript covers safer access patterns after parsing succeeds.