Parsing and Stringifying JSON

Since JSON is just text, JavaScript needs two built-in functions to move between "JSON as a string" and "JSON as real JavaScript values": JSON.parse and JSON.stringify.

const jsonText = '{"title":"Modern JavaScript","lessons":6,"tags":["js","dom"]}';

const course = JSON.parse(jsonText);
console.log(course.title);
console.log(course.tags[1]);

const backToText = JSON.stringify(course);
console.log(backToText);

const pretty = JSON.stringify(course, null, 2);
console.log(pretty);

Reading it

• JSON.parse(text) turns a JSON string into real JavaScript values (objects, arrays, numbers, ...), throws a SyntaxError if the text isn't valid JSON.
• JSON.stringify(value) turns a JavaScript value into a JSON string.
• The third argument to stringify, here 2, adds indentation, handy for logging or writing readable files, it has no effect on parsing.
• Anything JSON.stringify can't represent, functions, undefined values, gets silently dropped from objects (or turned into null inside arrays).

const withExtras = { name: 'Ada', greet: () => 'hi', missing: undefined, count: 3 };
console.log(JSON.stringify(withExtras)); // greet and missing both disappear