title	JSON
date	2021-09-14 11:26:55 -0700
background	bg-[#646464]
tags	config format
categories	Programming
intro	This is a quick reference cheat sheet for understanding and writing JSON format configuration files.
plugins	copyCode

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

{.marker-round}

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

Type	Description
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 {.row-span-3}

\"	Double quote
\\	Backslash
\/	Forward slash
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Tab
\u	Trailed by four hex digits

Examples

{
  "url": "https://cheatsheets.zip",
  "msg": "Hi,\n\"CheatSheets.zip\"",
  "intro": "Share quick reference and cheat sheet for developers."
}

Invalid String

{ "foo": "bar" }

Have to be delimited by double quotes

Number {.row-span-2}

Type	Description
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

Examples

{
  "positive": 12,
  "negative": -1,
  "fraction": 10.25,
  "exponent": 1.0e2,
  "zero": 0
}

Invalid Number

{ "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 {.row-span-2}

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 {.row-span-2}

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

Also see {.cols-1}

• JSON (json.org)
• JSON Editor Online (jsoneditoronline.org)
• Convert JSON Array to Markdown Table, CSV and more (tableconvert.com)