jsonDecode
- Dart course
- Advanced
- Lesson 37/83
- 5 min
Learn JSON parsing with jsonDecode.
jsonDecode
jsonDecode(String) comes from dart:convert and turns JSON text into a Dart object. The result is dynamic; usually cast to Map<String, dynamic> or List.
Example: var data = jsonDecode('{"name":"Ayşe","age":30}');. data['name'] yields 'Ayşe'. Malformed JSON throws FormatException.
Without a cast, data.name does not work; use data['name']. For type safety a fromJson factory is preferred (we will see it in L3).
Reading as a Map
A JSON object is cast to Map<String, dynamic>: var m = jsonDecode(s) as Map<String, dynamic>;. Then values are read via m['key'].
For nested objects, chain access: m['user']['name']. Each level is dynamic, so the compiler does not check; errors appear at runtime.
For lists, var list = jsonDecode(s) as List;. Elements are still dynamic; cast to a type.
Practice Decode JSON text and print it
Add import 'dart:convert';. Inside main add var data = jsonDecode('{"name":"Ayşe","age":30}');. Add print(data['name']);.
Starter code
void main() {
// add dart:convert import; decode JSON text; print name
}Sample solution
import 'dart:convert';
void main() {
var data = jsonDecode('{"name":"Ayşe","age":30}');
print(data['name']);
}Expected output
Ayşe
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does jsonDecode return?
- dynamic Correct answer
- Map
- String
- int
Explanation: jsonDecode returns dynamic; cast to Map/List.
2 Decode JSON text
var data = ____(jsonText);var data = jsonDecode(jsonText);Explanation: jsonDecode turns JSON text into a Dart object.
3 Match the jsonDecode parts
| Term | Meaning |
|---|---|
jsonDecode |
String → dynamic |
Map<String, dynamic> |
Object cast |
data['key'] |
Value access |
FormatException |
Malformed JSON |