JSON (JavaScript Object Notation) data format is widely used for data interchange. A JSON object is a key-value data format that is enclosed in curly braces. It is a human and machine readable format. JSON uses the .json file extension.
JSON file cannot have comment. The JSON should all be data, and if you include a comment, then it will be data too.
Syntax
Key-value pairs have a colon between them as in "key" : "value". Each key-value pair is separated by a comma. Keys are on the left side of the colon, and can be any valid string. Within each object, keys need to be unique. Below shows an example of JSON object.
{
"name" : "mymusing",
"location" : "Earth"
}Tokens used in JSON document are
- “: ” separate name from value
- “,” separate name-value pairs
- “{” and “}” define an object
- “[” and “]” define an array
Below shows example of nested object with array. Object color is nested within colors object. colors object has list of color object.
{
"colors" : [
{
"color" : "Red"
},
{
"color" : "Blue"
},
{
"color" : "Green"
}
]
}Data Types
JSON values are found to the right of the colon. At the granular level, JSON supports below data types
- String
- Number
- Boolean
- Null/empty
- Object
- Array
String are sequence of characters, inserted between ” and “.
{
"color" : "Red"
}Number are represented in base 10 with no leading zero. It can be a fraction (e.g. .5). It can also have an exponent of 10, prefixed by e.
{
"number_positive" : 10,
"number_negative" : -10,
"number_fraction" : 1.05,
"number_exponent" : 15.0E+2
}Boolean value can be either true or false. If no value to assign. it can be treated as null.
{
"boolean_type" : true
"null_type" : ,
}Object are unordered set of name/value pairs inserted between {} (curly braces). Multiple name/value pairs are separated by a , (comma). Array is ordered collection of values. It begins with [ (left bracket) and ends with ] (right bracket). It’s values are separated by , (comma).
{
"object_type": {
"color" : "Red"
},
"ids" : [1,2,3]
}Accessing Object Values
JSON objects are very much like javascript objects. Keys must be strings, and values must be a valid JSON data type (string, number, object, array, boolean or null). Object values can be accessed in two ways:
- Dot (.) notation
- Bracket ([]) notation
To loop through object values use for loop, just like looping through an array.
var num = {
"number_positive" : 10,
"number_negative" : -10,
"number_fraction" : 1.05,
"number_exponent" : 15.0E+2,
"number_array" : [1, 2, 3 ,4, 5]
}
// Output : 10
console.log( num.number_positive );
// Output : 10
console.log( num["number_positive"]);
// Output : 1
console.log( num["number_array"][0]);
/* Output:
number_positive - 10
number_negative - -10
number_fraction - 1.05
number_exponent - 1500
number_array - 1,2,3,4,5
*/
for (x in num)
{
console.log(x + " - " + (num[x]));
}