What makes JSON.parse so particular about quotes?

My journey began with the attempt to create an object like this using JSON.parse():

a = {x:1} 
// -> Object {x: 1}

Instinctively, I initially tried:

a = JSON.parse('{x:1}')
// -> Uncaught SyntaxError: Unexpected token x

After some trial and error, I discovered:

a = JSON.parse('{"x":1}')
// -> Object {x: 1}

However, when I mistakenly altered the syntax, confusion ensued:

a = JSON.parse("{'x':1}")
//-> Uncaught SyntaxError: Unexpected token '

This led me to question why

  1. the necessity of quoting property names in JSON.parse()
  2. the inconsistency in accepting single quotes but rejecting double quotes in the implementation

Answer №1

One common source of confusion arises from the distinction between JSON and JavaScript objects.


JSON (JavaScript Object Notation) serves as a data format designed for easy data exchange in a streamlined manner, hence its adherence to a single valid syntax. This simplifies the parsing process significantly. More details can be found on the official JSON website.

Key points about JSON:

  • Keys must be enclosed in quotes using "
  • Values can be strings, numbers, objects, arrays, booleans, or "null"
  • String values need quotes around them with "

JavaScript objects, on the other hand, have a connection to JSON but are not identical. While valid JSON is also a valid JavaScript object, the reverse is not always true.

Consider this:

  • Both keys and values can be quoted using either " or '
  • Keys do not necessarily require quotes
  • Values might consist of functions or other JavaScript objects

Answer №2

It was mentioned in the remarks that this is because it's according to the JSON specification. This decision is made because JSON is designed to function as a language-independent data exchange format. In many programming languages, including those with hash literals, unquoted strings are not permitted as keys in a hash table.

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