JSON

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

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

\" 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://quickref.me",
  "msg" : "Hi,\n\"QuickRef.ME\"",
  "intro": "Share quick reference and cheat sheet for developers."
}

#Invalid String

{ "foo": 'bar' }

Have to be delimited by double quotes

#Number

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" : 1.0E+2,
  "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] {"fist": "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