JSON Parsing and Serialization in JavaScript

In JavaScript, handling JSON data is a very common operation, mainly involving two core methods:

1. JSON Parsing

The JSON.parse() method is used to convert a JSON string into a JavaScript object.

Basic Usage

javascript
const jsonString = '{"name": "John", "age": 30, "city": "New York"}';
const obj = JSON.parse(jsonString);
console.log(obj.name); // Output: John

Advanced Usage: Using reviver Function

JSON.parse() can accept a second parameter as a reviver function, used to transform the result during parsing:

javascript
const jsonString = '{"name": "John", "birthDate": "2000-01-01"}';
const obj = JSON.parse(jsonString, (key, value) => {
  if (key === 'birthDate') {
    return new Date(value);
  }
  return value;
});
console.log(obj.birthDate instanceof Date); // Output: true

2. JSON Serialization

The JSON.stringify() method is used to convert a JavaScript object into a JSON string.

Basic Usage

javascript
const obj = {name: "John", age: 30, city: "New York"};
const jsonString = JSON.stringify(obj);
console.log(jsonString); // Output: {"name":"John","age":30,"city":"New York"}

Advanced Usage

2.1 Using replacer Parameter

You can specify which properties to include, or transform values:

javascript
const obj = {name: "John", age: 30, city: "New York", salary: 50000};
// Include only specified properties
const jsonString1 = JSON.stringify(obj, ['name', 'age']);
// Transform values using function
const jsonString2 = JSON.stringify(obj, (key, value) => {
  if (key === 'salary') {
    return value > 0 ? 'confidential' : value;
  }
  return value;
});

2.2 Using space Parameter

Used to add indentation and whitespace, making the output more readable:

javascript
const obj = {name: "John", age: 30, city: "New York"};
const jsonString = JSON.stringify(obj, null, 2);
// Outputs formatted JSON string with 2-space indentation

Notes

1. Circular References：If there are circular references in the object, JSON.stringify() will throw an error.
2. undefined and Functions：These values are ignored (in objects) or converted to null (in arrays) during serialization.
3. Date Objects：Will be converted to ISO-formatted strings.
4. Regular Expressions：Will be converted to empty objects {}.
5. Symbols：When used as object keys, they are ignored; when used as values, they are converted to undefined.