JSON.Stringify on second argument

Source: Dev.to

Syntax

JSON.stringify(value, replacer, space);

• value – The JavaScript value to be converted (object, array, string, number, etc.).
• replacer (optional) – A function or array that transforms the value before stringification.
• space (optional) – A string (or number) used to indent the output for readability.

What it Does

• Converts primitive values like strings, numbers, booleans, and null directly to their JSON equivalents.
• Converts arrays by iterating through their elements and stringifying each one.
• Converts objects by enumerating their properties and stringifying their key‑value pairs.
• Excludes properties with undefined values or functions by default.
• Can be customized with the replacer and space options.

Examples

Basic usage

const object = { name: "Alice", age: 30 };
JSON.stringify(object); // '{"name":"Alice","age":30}'

const array = [1, 2, 3];
JSON.stringify(array); // '[1,2,3]'

const date = new Date();
JSON.stringify(date); // '"2024-02-07T02:54:22.394Z"' (not recommended)

Using a replacer function to exclude a property

const object = { name: "Alice", age: 30, password: "secret" };
const jsonString = JSON.stringify(object, (key, value) => {
  if (key === "password") return undefined; // Exclude password
  return value;
});
// '{"name":"Alice","age":30}'

Filtering properties with a replacer array

const objects = [
  { name: "Eka Prasetia" },
  { city: "Jakarta" },
  { hobby: "Play codes" },
];

JSON.stringify(objects, ["name", "hobby"], 2);
// [
//   {
//     "name": "Eka Prasetia"
//   },
//   {},
//   {
//     "hobby": "Play codes"
//   }
// ]

Replacing property values with a replacer function

const result = JSON.stringify(
  objects,
  (key, value) => {
    if (key.match(/name|city/)) return "👨‍👩‍👧✌";
    return value;
  },
  2
);
// [
//   {
//     "name": "👨‍👩‍👧✌"
//   },
//   {
//     "city": "👨‍👩‍👧✌"
//   },
//   {
//     "hobby": "Play codes"
//   }
// ]

The second argument (replacer) can be a function that is called for each property. It may return a new value (string, number, etc.) to replace the original, or undefined to omit the property from the output.

Key Points

• JSON.stringify() is useful for sending data to servers or storing it in local storage.
• Be mindful of circular references or functions when stringifying objects.
• Use a replacer to customize the output or exclude sensitive information.
• Avoid stringifying Date objects directly, as JSON has no native date type.

Happy coding! 🔥