JSON schema with single quote in property name fails to be processed when the property is required

[tomastauer]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

5.14.1

Plugin version

No response

Node.js version

20.11.0

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

22.04.4

Description

When stringifying JSON schema that has a single quote character (') in the name of the property and the property is required at the same time, the generated function is syntactically incorrect and the process fails.

Steps to Reproduce

const fastJson = require('fast-json-stringify');

const schema = {
	title: 'Example Schema',
	type: "object",
	properties: {
		"'": {
			type: "string",
		},
	},
	required: [
		"'",
	],
};

fastJson(schema, {});

will fail with

 SyntaxError: missing ) after argument list
        at new Function (<anonymous>)

as the code the schema is translated to is as follows:

let json = '{'

      if (obj[\"'\"] !== undefined) {
        
        json += \"\\\"'\\\":\"
        
        if (typeof obj[\"'\"] !== 'string') {
          if (obj[\"'\"] === null) {
            json += '\"\"'
          } else if (obj[\"'\"] instanceof Date) {
            json += '\"' + obj[\"'\"].toISOString() + '\"'
          } else if (obj[\"'\"] instanceof RegExp) {
            json += serializer.asString(obj[\"'\"].source)
          } else {
            json += serializer.asString(obj[\"'\"].toString())
          }
        } else {
          json += serializer.asString(obj[\"'\"])
        }
        
      } else {
        throw new Error('\"'\" is required!')
        ==================^^==== here is the problem, the single quote is unescaped and collides with the single quotes used to wrap the error message
      }
      
    return json + '}'

Expected Behavior

Schema is accepted and stringified. It should be enough to escape the single quote character (') in the generated error message.

Expected output of the generated functions would be

  throw new Error('\"\\'\" is required!')