JSON Quick Dev Reference

This is a quick reference cheat sheet for understanding and writing JSON format configuration files.

Getting Started

Introduction

JSON is a lightweight text-based open standard designed for human-readable data interchange.

JSON stands for JavaScript Object Notation JSON is easy to read and write. JSON is language agnostic data-interchange format JSON filename extension is .json JSON Internet Media type is application/json

Examples

{
  "name": "Jason",
  "age": 39,
  "height": 1.92,
  "gender": "M",
  "salary": 70000,
  "married": true,
  "children": [
    {"name": "Tom", "age": 9, "gender":"M"},
    {"name": "Ava", "age": 7, "gender":"F"}
  ]
}

Types

Number — Double precision floating-point

String — Series of characters

Boolean — true or false

Array — Ordered sequence of values

Value — String, Number, Boolean, null etc

Object — Unordered collection of key/value pairs

null — Null or Empty

String

\" — Double quote

\\ — Backslash

\/ — Forward slash

\b — Backspace

\f — Form feed

\n — Newline

\r — Carriage return

\t — Tab

\u — Trailed by four hex digits

{
  "url": "https://ref.softcrony.com",
  "msg" : "Hi,\n\"Ref.Softcrony.COM\"",
  "intro": "Share tech reference and cheat sheet for developers."
}

{ "foo": 'bar' }

Have to be delimited by double quotes

Number

Integer — Digits 1-9, 0 and positive or negative

Fraction — Fractions like 0.3, 3.9

Exponent — Exponent like e, e+, e-, E, E+, E

{
  "positive" : 12,
  "negative" : -1,
  "fraction" : 10.25,
  "exponent" : 1.0E+2,
  "zero" : 0
}

{ "foo": 0xFF }

In JSON you can use only Decimal Literals

Objects

{
  "color": "Purple",
  "id": "210",
  "composition": {
    "R": 70,
    "G": 39,
    "B": 89
  },
  "empty_object": {}
}

Multiple key/value pairs separated by a comma

Arrays

[1, 2, 3, 4, 5]

Begins with [ and ends with ]

Array of objects

{
  "children": [
    {"name": "Jimmy Smith", "age": 15},
    {"name": "Sammy Sosa", "age": 12}
  ]
}

Object of arrays

{
  "attributes": ["a1", "a2"],
  "methods": ["getter", "setter"],
  "empty_array": []
}

2D Array

{
  "my_sequences": [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9, 0],
    [10, 11]
  ]
}

Object of objects

{
  "Mark McGwire": {
    "hr": 65,
    "avg": 0.278
  },
  "Sammy Sosa": {
    "hr": 63,
    "avg": 0.288
  }
}

Nested

{
  "Jack": {
    "id": 1,
    "name": "Franc",
    "salary": 25000,
    "hobby": ["a", "b"],
    "location": {
        "country": "A", "city": "A-A"
    }
  }
}

Access JSON in JavaScript

Access Object

let myObject = {
  "name": "Jason",
  "last": "Doe",
  "age": 39,
  "gender": "M",
  "salary": 70000,
  "married": true
};

myObject.name — "Jason"

myObject["name"] — "Jason"

myObject.age — 39

myObject.other — undefined

myObject[0] — undefined

Access Nested

let myObject = {
  "ref": {
    "name": 0,
    "last": 1,
    "age": 2,
    "gender": 3,
    "salary": 4,
    "married": 5
  },
  "jdoe": [
    "Jason",
    "Doe",
    39,
    "M",
    70000,
    true
  ],
  "jsmith": [
    "Tom",
    "Smith",
    42,
    "F",
    80000,
    true
  ]
};

myObject.ref.age — 2

myObject["ref"]["age"] — 2

myObject.jdoe — ["Jason", "Doe", 39 ...]

myObject.jsmith[3] — "F"

myObject[1] — undefined

Access Array of Objects

let myArray = [
  {
    "name": "Jason",
    "last": "Doe",
    "age": 39,
    "gender": "M",
    "salary": 70000,
    "married": true
  },
  {
    "name": "Tom",
    "last": "Smith",
    "age": 42,
    "gender": "F",
    "salary": 80000,
    "married": true
  },
  {
    "name": "Amy",
    "last": "Burnquist",
    "age": 29,
    "gender": "F",
    "salary": 60000,
    "married": false
  }
];

myArray[0] — {"name": "Jason", ...}

myArray[1].name — "Tom"

myArray[1][2] — 42

myArray[3] — undefined

myArray[3].gender — TypeError: Cannot read...

Access Array

let myArray = [
  "Jason",
  "Doe",
  39,
  "M",
  70000,
  true
];

myArray[1] — "Doe"

myArray[5] — true

myArray[6] — undefined