What are the Key Differences Between JavaScript Object Literal Notation and JSON?

Object Literal Notation vs. JSON: Understanding the Key Differences

In JavaScript, we have two similar yet distinct ways to define objects: Object Literal Notation and JSON (JavaScript Object Notation). While they share some syntactic similarities, they differ in fundamental ways.

Definition of JSON

JSON (pronounced "jason") is a language-independent text format for representing structured data. It is designed for efficient data exchange between applications and systems.

Key Differences

1. Key Syntax:

• JSON: Keys must be strings enclosed in double quotes (").
• JavaScript Object Literal: Keys can be strings, numbers, or identifiers (without quotes).

2. Value Types:

• JSON: Supports a limited set of value types: strings, numbers, objects, arrays, booleans, and null.
• JavaScript Object Literal: Allows any valid JavaScript expression as a value, including functions.

3. Duplicates and Undefined:

• JSON: Duplicate keys produce undefined, unpredictable results.
• JavaScript Object Literal: Duplicate keys produce defined results; in loose mode, the latter value overwrites the former, while in strict mode, it raises an error.

4. Function Definitions:

• JSON: Does not have a syntax for defining functions.
• JavaScript Object Literal: Allows assigning functions to properties.

Example

Consider the following code snippet:

var anObject = {
    property1 : true,
    showMessage : function (msg) { alert(msg) }
};

According to JSON syntax, this code is not a valid JSON object because:

• The keys are not strings enclosed in quotes.
• The value for showMessage is a function definition, which is not allowed in JSON.

Conclusion

While Object Literal Notation and JSON share some similarities, they are distinct data formats with important differences. JSON is a standardized text format for data exchange, while JavaScript Object Literals are native JavaScript constructs used for representing data within a program.

The above is the detailed content of What are the Key Differences Between JavaScript Object Literal Notation and JSON?. For more information, please follow other related articles on the PHP Chinese website!