PetexSpace

JSON Cheatsheet

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

TypeDescription
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

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

TypeDescription
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

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

Also see

Adapted from Fechin/referenceGPL-3.0 licenseMarkdown sourceChanges and attribution