Difference between 'object' and {} in TypeScript

Question

Trying to figure out the difference between these 2 types in TypeScript:

foo: object

and

bar: {}?

---

Exa

Answer 1

The following example shows how different types of object behave differently:

var o: object;
o = { prop: 0 }; // OK
o = []; // OK
o = 42; // Error
o = "string"; // Error
o = false; // Error
o = null; // Error
o = undefined; // Error

var p: {}; // or Object
p = { prop: 0 }; // OK
p = []; // OK
p = 42; // OK
p = "string"; // OK
p = false; // OK
p = null; // Error
p = undefined; // Error

var q: { [key: string]: any };
q = { prop: 0 }; // OK
q = []; // OK
q = 42; // Error
q = "string"; // Error
q = false; // Error
q = null; // Error
q = undefined; // Error

var r: { [key: string]: string };
r = { prop: 'string' }; // OK
r = { prop: 0 }; // Error
r = []; // Error
r = 42; // Error
r = "string"; // Error
r = false; // Error
r = null; // Error
r = undefined; // Error

With that we can tell:

• {} which is the same as type Object is the least specific. You can assign objects, arrays and primitives to it.
• object is more specific and is similar to { [key: string]: any }. You can assign objects and arrays to it, but not primitives.
• { [key: string]: string } is the most specific, that doesn't allow any primitive types, arrays or objects with a non-string value to be assigned to it.

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