Chapter 11: JSON (The Universal Language)

Goal: Learn how to trade data with the outside world. Concept: Your Go program sends structs. The Browser wants JSON (JavaScript Object Notation). We need a translator.

1. The Sticker (Struct Tags)

We learned about Structs (The Blueprint). But how does Go know that BookTitle in Go code should be title in JSON? Tags. Think of them as sticky notes attached to the fields for the translator to read.

type Book struct {
    Title  string  `json:"title"`       // lowercase "title" in JSON
    Price  float64 `json:"price"`
    Hidden string  `json:"-"`           // Ignore this field!
}

2. Marshaling (Packing)

Marshal = Converting Go Struct -> JSON String. (Ideally, a byte slice, but think of it as text).

myBook := Book{Title: "Go Guide", Price: 19.99}
jsonData, err := json.Marshal(myBook)
if err != nil {
    log.Fatal(err)
}
fmt.Println(string(jsonData))
// Output: {"title":"Go Guide","price":19.99}

3. Unmarshaling (Unpacking)

Unmarshal = JSON String -> Go Struct.

jsonStr := `{"title":"Go Guide","price":19.99}`
var newBook Book
err := json.Unmarshal([]byte(jsonStr), &newBook)

4. Visual Signal: The Translator 🗣️

• Go: Speaks "Binary/Structs".
• Web: Speaks "Text/JSON".
• encoding/json: The interpreter standing in the middle, reading the Sticky Notes (Tags) to know what to say.

Why do we care?

When you build your API in the next level, every single request will involve:

1. Unmarshaling user Input (JSON -> Struct).
2. Marshaling your Response (Struct -> JSON).