Why can a function be defined in JSON?

Question

I am reading a React doc, https://reacttraining.com/react-router/web/example/auth-workflow, and trying to understand the following piece of code:

Looks like a the function definition happens in a json object, but my understanding is that we can't have funciton inside json

const fakeAuth = {
  isAuthenticated: false,
  authenticate(cb) {
    this.isAuthenticated = true;
    setTimeout(cb, 100); // fake async
  },
  signout(cb) {
    this.isAuthenticated = false;
    setTimeout(cb, 100);
  }
};

That's **not** JSON, which requires double quotes for key names (and string values). — jonrsharpe, Jun 19 '18 at 21:25
JSON is a **string** format - you have an actual Javascript object, not a string with JSON encoded data! — Mörre, Jun 19 '18 at 21:28
@Prathibha The posted code is Javascript (post ES 2015 level code). React code is Javascript plus JSX, the latter is not in OPs example. — Mörre, Jun 19 '18 at 21:31
@jonrsharpe Even if the example had double quotes around the keys it would not be JSON but still a JS object, because JSON is a **string** format. — Mörre, Jun 19 '18 at 21:34
Possible duplicate of [What is the difference between JSON and Object Literal Notation?](https://stackoverflow.com/q/2904131/218196) — Felix Kling, Jun 20 '18 at 00:14
**Context** is what matters. What you have is JavaScript code, not JSON. While some parts of the syntax look similar, they are two different things. Think about it as two different languages. Consider JavaScript and C: `'foo'` is valid in JavaScript because strings can be single quoted, but it's not valid in C because single quotes denote single characters (i.e. you can only have `'f'`). — Felix Kling, Jun 20 '18 at 00:18

score 1 · Answer 1 · answered Jun 19 '18 at 21:25

1

In true JSON you cannot have a function, and there are no vars. It's a format just used to hold data (based on JavaScript). You can have a function that is a property of an Object in JavaScript.

answered Jun 19 '18 at 21:25

StackSlave

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score 1 · Answer 2 · answered Jun 19 '18 at 21:28

1

if you are referring to the whole const fakeAuth = {...} code, that is not a JSON object.. rather that is a creating a fakeAuth object has a property (isAuthenticated) and functions with parameters(authenticate, signout)

answered Jun 19 '18 at 21:28

jmesolomon

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I think he's referring to `authenticate(cb) { ... }` – Barmar Jun 19 '18 at 21:29

score 1 · Accepted Answer · answered Jun 19 '18 at 21:31

As mentioned in the comments, this isn't JSON, it's a Javascript object literal. It's using the ES6 shorthand syntax for function properties.

authenticate(cb) {
  this.isAuthenticated = true;
  setTimeout(cb, 100); // fake async
},

is short for:

authenticate: function(cb) {
  this.isAuthenticated = true;
  setTimeout(cb, 100); // fake async
},

Why can a function be defined in JSON?

3 Answers3