JSON Parse Error Syntax Error Unexpected token N In JSON

You will see following error if json String contains values other string or numbers. For example it can happen if you are parsing the data from the Ajax request.

In [1]:

let jsonString = '{"name":"John", "age": 5, "name":"Alex", "age":NaN}';

In [2]:

JSON.parse(jsonString);

undefined:1
{"name":"John", "age": 5, "name":"Alex", "age":NaN}
                                               ^

SyntaxError: Unexpected token N in JSON at position 47
    at JSON.parse (<anonymous>)
    at evalmachine.<anonymous>:1:6
    at Script.runInThisContext (node:vm:129:12)
    at Object.runInThisContext (node:vm:305:38)
    at run ([eval]:1020:15)
    at onRunRequest ([eval]:864:18)
    at onMessage ([eval]:828:13)
    at process.emit (node:events:526:28)
    at emit (node:internal/child_process:938:14)
    at processTicksAndRejections (node:internal/process/task_queues:84:21)

To fix this remove the value which is not a string or number. We can replace the value with null, null is valid keyword.

In [3]:

let cleanedJsonString = jsonString.replace(/NaN/g, 'null');

Let us try now to parse the cleaned json string.

In [4]:

JSON.parse(cleanedJsonString);

Out[4]:

{ name: 'Alex', age: null }

JSON Parse Error Syntax Error Unexpected token N In JSON

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