JSON

JSON = JavaScript Object Notation for data exchange

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What is JSON?

"Data format based on JavaScript objects"

JSON (JavaScript Object Notation) is a lightweight data interchange format.

"JSON is a text-based data format derived from JavaScript object syntax, used for data exchange between systems."

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JSON Syntax

Similar to JavaScript objects

{
  "name": "John",
  "age": 30,
  "isActive": true,
  "hobbies": ["reading", "coding"],
  "address": {
    "city": "New York",
    "country": "USA"
  }
}

"JSON syntax is similar to JavaScript objects but with stricter rules - keys must be strings in double quotes."

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JSON vs JavaScript Objects

JSON = subset, stricter rules

Feature	JSON	JavaScript
Keys	Must be strings	Can be identifiers
Quotes	Double quotes only	Single or double
Values	Limited types	Any JavaScript value
Comments	Not allowed	Allowed
Functions	Not allowed	Allowed

"JSON is a subset of JavaScript - stricter rules, no functions, no comments, keys must be double-quoted strings."

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JSON.parse()

Convert JSON string to object

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

"JSON.parse converts a JSON string into a JavaScript object."

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JSON.stringify()

Convert object to JSON string

const obj = { name: "John", age: 30 };
const jsonString = JSON.stringify(obj);
console.log(jsonString); // '{"name":"John","age":30}'

"JSON.stringify converts a JavaScript object into a JSON string."

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Supported Data Types

Primitives + objects + arrays

JSON supports:

• Strings
• Numbers
• Booleans
• null
• Objects
• Arrays

Not supported:

• Functions
• undefined
• Symbols
• Dates (become strings)

"JSON supports primitives, objects, and arrays, but not functions, undefined, symbols, or Date objects."

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Common Use Cases

API communication · Storage · Configuration

• API requests/responses: Data exchange
• localStorage: Store data as JSON
• Configuration files: JSON configs
• Data serialization: Convert objects to strings

"JSON is used for API communication, localStorage storage, configuration files, and data serialization."

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Replacer Function

Filter properties in stringify

const obj = { name: "John", age: 30, password: "secret" };

const json = JSON.stringify(obj, (key, value) => {
  if (key === "password") return undefined; // Exclude
  return value;
});

"JSON.stringify accepts a replacer function to filter or transform properties during serialization."

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9️⃣ Reviver Function

Transform values in parse

const json = '{"date":"2023-01-01"}';

const obj = JSON.parse(json, (key, value) => {
  if (key === "date") return new Date(value);
  return value;
});

"JSON.parse accepts a reviver function to transform values during parsing."

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Error Handling

Try-catch for invalid JSON

try {
  const obj = JSON.parse(invalidJson);
} catch (error) {
  console.error("Invalid JSON:", error);
}

"Always use try-catch when parsing JSON, as invalid JSON throws errors."

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"JSON is a data format based on JavaScript objects, used for data exchange. It has stricter rules - double-quoted keys, no functions or comments. JSON.parse converts strings to objects, JSON.stringify converts objects to strings. JSON supports primitives, objects, and arrays. Use replacer/reviver functions for transformation. Always handle parsing errors."

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🧠 Ultra-Short Cheat Sheet

Data interchange format
JSON.parse (string → object)
JSON.stringify (object → string)
Stricter than JavaScript
No functions, undefined, dates
API communication
localStorage
Error handling