JSON, references

JavaScript Object Notation (JSON) is a data-interchange format. Although not a strict subset, JSON closely resembles a subset of JavaScript syntax. Though many programming languages support JSON, it is especially useful for JavaScript-based apps, including websites and browser extensions.
MDN: Working with JSON
MDN: JSON object
JSON.org: Introducing JSON

Notes about JSON

JSON is purely a string with a specified data format — it contains only properties, no methods.
JSON requires double quotes to be used around strings and property names. Single quotes are not valid other than surrounding the entire JSON string.
Even a single misplaced comma or colon can cause a JSON file to go wrong, and not work. You should be careful to validate any data you are attempting to use (although computer-generated JSON is less likely to include errors, as long as the generator program is working correctly). You can validate JSON using an application like JSONLint.
JSON can actually take the form of any data type that is valid for inclusion inside JSON, not just arrays or objects. So for example, a single string or number would be valid JSON.
Unlike in JavaScript code in which object properties may be unquoted, in JSON only quoted strings may be used as properties.

The JSON object has the following static methods:

JSON.parse(text[, reviver]) Accepts a JSON string as a parameter, and returns the corresponding JavaScript object.

Parse the string text as JSON, optionally transform the produced value and its properties, and return the value. Any violations of the JSON syntax, including those pertaining to the differences between JavaScript and JSON, cause a SyntaxError to be thrown. The reviver option allows for interpreting what the replacer has used to stand in for other datatype.
JSON.stringify(value[, replacer[, space]]) Accepts an object as a parameter, and returns the equivalent JSON string.

Return a JSON string corresponding to the specified value, optionally including only certain properties or replacing property values in a user-defined manner. By default, all instances of undefined are replaced with null, and other unsupported native data types are censored. The replacer option allows for specifying other behavior.
Create a deep copy of an object/array (remember the Arrays are Objects too):
```
  const newObject = JSON.parse(JSON.stringify(existingObject));
```