CODEWITHSUNDEEP
javascripttypes
madechai
madechai

Reputation: 111

Can javascript variables contain anything?

I know they can contain primitive data types and objects. And since I've been programming in react, I know they can contain objects, components, and even json. Is there any limitations on javascript variables? var/const/let

Upvotes: 1

Views: 196

Answers (2)

T.J. Crowder
T.J. Crowder

Reputation: 1074425

Any value can be stored in a JavaScript variable. Values include:

  • All primitives
  • Object references

Almost everything is an object in JavaScript. Notably, functions are objects (including React stateless functional components [SFCs] and React components, which are constructor functions), and so a variable can contain a reference to a function:

function foo(msg) {
    console.log("foo: " + msg);
}
function bar(msg) {
    console.log("bar: " + msg);
}
const f = Math.random() < 0.5 ? foo : bar;
f("Hi");

You have a 50/50 chance of seeing "foo: Hi" or "bar: Hi" with that code.

There are only a few things I can think of that a variable cannot contain:

  • Operators. E.g. this is not valid:

    // NOT VALID
const op = Math.random() < 0.5 ? + : -;
console.log(10 op 5);

    ...although it's easy to get the same effect with functions:

    const op = Math.random() < 0.5
           ? (a, b) => a + b
           : (a, b) => a - b;
console.log(op(10, 5));

  • Execution contexts or lexical environments, but only because nothing ever exposes a reference to them in code.

  • Memory locations, because (again) nothing ever exposes them in code.

...and even json

JSON is a textual notation for data exchange. (More here.) If you're dealing with JavaScript source code, and not dealing with a string, you're not dealing with JSON.

Upvotes: 3

Jeremi G
Jeremi G

Reputation: 421

Variables are the way to address all objects. JavaScript is an Object-based language (String, Number, etc. are all Objects with different prototypes).

For example, a var can hold: true, undefined, null, "string", `template`, {}, [], NaN, 7, infinity, /abc/

There aren'y any limitations I can think of.

Upvotes: 0

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