How to implement JSON.stringify?

Implementing a custom JSON.stringify function is a complex task, as the standard JavaScript JSON.stringify handles various data types and edge cases. However, we can create a simplified version to understand the core concepts.

Here's how you can approach a basic implementation:

1. Handle Basic Types:

- Start by handling primitive data types like strings, numbers, booleans, and null.

2. Handle Arrays:

- Iterate through the array and recursively call the stringify function for each element. Enclose the result in square brackets [].

3. Handle Objects:

- Iterate through the object properties and recursively call the stringify function for each value. Enclose the result in curly braces {} with the key-value pairs separated by colons :.

4. Recursive Approach:

- The implementation will be recursive since an object or array may contain other nested objects and arrays.

5. Handle Special Values:

- Be mindful of special values like undefined, NaN and Infinity. The JSON.stringify function will normally return null for undefined and also handle numeric infinity values appropriately.

6. The Code:

function myStringify(obj) {
  if (obj === null) {
   return "null";
  }
  if (typeof obj === "boolean") {
   return obj ? "true" : "false";
  }
  if (typeof obj === "number") {
   return isFinite(obj) ? String(obj) : "null";
  }
  if (typeof obj === "string") {
   return `"` + obj.replace(/"/g, '\\"') + `"`;
  }
  if (typeof obj === "undefined" || typeof obj === "function"){
   return undefined;
  }
  if (Array.isArray(obj)) {
   let result = "[";
   for (let i = 0; i < obj.length; i++) {
   let element = myStringify(obj[i]);
   result += element === undefined ? "null" : element;
   if (i < obj.length - 1) result += ",";
   }
   result += "]";
   return result;
  }
  if (typeof obj === "object") {
   let result = "{";
   let keys = Object.keys(obj);
   for (let i = 0; i < keys.length; i++) {
    let key = keys[i];
    let value = myStringify(obj[key]);
    if(value !== undefined) {
     result += `"` + key + `":` + value;
     if (i < keys.length - 1) result += ",";
   }
   }
   result += "}";
   return result;
  }
  return undefined;
}

Example Usage:

const myObject = { name: "John", age: 30, isStudent: false, courses: ["Math", "English"] };
const jsonString = myStringify(myObject);
console.log(jsonString); // Output: {"name":"John","age":30,"isStudent":false,"courses":["Math","English"]}

This simplified implementation demonstrates the basic logic of how JSON.stringify works. Note that a complete implementation of JSON.stringify includes handling more complex cases, such as circular references, which are not addressed in this basic example.

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