レッスン 4
Objects and Arrays 日本語ガイド
日本語の json objects and arrays ガイド: Nested structures, key naming, and modeling real-world data.
このコンテンツはまだ日本語で用意されていません。ローカライズが完了するまで English 版を表示しています。
Most real JSON documents combine objects and arrays to represent entities and collections. Designing clear shapes makes APIs and configs easier to consume.
Objects as records
An object often models one thing—a user, an order, a settings block:
{
"userId": "u_42",
"email": "[email protected]",
"preferences": {
"theme": "dark",
"notifications": true
}
}
Nested objects group related fields without flattening names like preferences_theme.
Arrays as lists
Arrays model ordered collections: tags, line items, search results:
{
"tags": ["json", "api", "tutorial"],
"items": [
{ "sku": "A1", "qty": 2 },
{ "sku": "B3", "qty": 1 }
]
}
Key naming conventions
JSON keys are case-sensitive. Common styles:
- camelCase —
firstName(typical in JavaScript APIs) - snake_case —
first_name(common in Python/Ruby backends) - kebab-case — rare inside keys because
-is minus; often avoided
Pick one style per API and stay consistent.
Empty structures
Both are valid and mean different things:
{ "list": [] }
{ "list": {} }
[] is an empty array; {} is an empty object. Do not interchange them unless your schema allows both.
Depth and readability
Deep nesting (a.b.c.d.e) mirrors data but hurts readability. Many teams flatten with clear key names or paginate large arrays. When reading unfamiliar JSON, start at the top level, expand one object or array at a time, and note repeating patterns—that is how most API payloads are designed.