JavaScript - why is number literal a valid JSON to parse and string is not?

JSON.parse() method expects a string but it doesn't wrap the argument inside the string with additional quotation marks.

In short, you can JSON.parse() everything you can assign to a variable.

Trying to JSON.parse('123abc') is like you were trying to assign a string to a variable like that:

xxxxxxxxxx

const x  = 123abc;

It needs to be wrapped with quotation marks to be a valid code:

xxxxxxxxxx

const x  = "123abc";

The same goes for the argument of the JSON.parse() method:

xxxxxxxxxx

JSON.parse('123');

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JSON.parse('"123abc"');

References

1. JSON.parse() - JavaScript | MDN