Strings and Numbers

Learning Focus

Strings and numbers are the most frequently used JSON primitives. Getting their encoding exactly right prevents the majority of common parser errors.

Strings

A JSON string is a sequence of Unicode characters enclosed in double quotes.

{
  "simple":      "Hello, World!",
  "withQuotes":  "She said "hello"",
  "withSlash":   "C:\Users\alice",
  "newline":     "Line 1
Line 2",
  "tab":         "Col1	Col2",
  "unicode":     "\u0041\u0042\u0043 (ABC via unicode escapes)",
  "empty":       ""
}

Common String Patterns

Use Case	Encoding
Date	"2024-01-15T08:30:00Z" (ISO 8601)
UUID	"550e8400-e29b-41d4-a716-446655440000"
Binary data	"SGVsbG8gV29ybGQ=" (Base64)
Large integer	"9007199254740993" (send as string)

Numbers

JSON has a single number type — no distinction between int, float, long.

{
  "integer":    42,
  "negative":  -17,
  "float":      3.14159,
  "scientific": 1.5e10,
  "negExp":     2.8E-4
}

Invalid Formats (RFC 8259)

0xFF    ✗  hexadecimal
0755    ✗  octal
007     ✗  leading zero
+42     ✗  explicit plus
.5      ✗  no leading digit
NaN     ✗  not supported
Infinity✗  not supported

IEEE 754 Precision Warning

JavaScript parses JSON numbers as 64-bit doubles. Integers above 2^53 - 1 silently lose precision:

{ "id": 9007199254740993 }

→ JavaScript reads 9007199254740992. Fix: transmit large integers as strings.

Concept Map

Concept Flow

JSON Primitives
  ├── String → Double-quoted Unicode + Escape sequences
  └── Number
        ├── Integer / Float / Scientific notation
        └── IEEE 754 Precision Limits (> 2^53 use strings)

Common Pitfalls

Pitfall	Consequence	Prevention
Single-quoted strings	Parse error	Always use "
Leading zeros	Parse error	Use 0, not 007
Large int as number	Silent precision loss in JS	Use strings for IDs > 2^53
NaN / Infinity	Parse error	Substitute null

What's Next

• Next: Booleans and Null — The remaining primitives and type coercion traps.
• Section Overview — Return to the Data Types module index.