As I delve into learning TypeScript, I frequently encounter the use of index signatures in function parameters. For example,
export function template(resources: {[key: string]: any})
Given that the value type is any, what is the utility of this type? Is there a distinction between utilizing any versus passing object as the type?
The `object` type in JavaScript is essentially just a native `Object`. It contains only the functions and keys that are associated with the built-in `Object`.
If you attempt to access a property of an `object` type, it will result in an error being thrown.
let b: object = {foo: 123};
b.foo; // Property 'foo' does not exist on type 'object'.
However, using `{[key: string]: any}` allows you to achieve the same functionality.
let a: {[key: string]: any} = {foo: 123};
a.foo;
The same can be done with `Record
In fact, the `Record` type is defined as `type Record
There are numerous ways to represent 'objects', with examples like Object, object, {}, { [k: T]: U }, and Record<K, T>. This is because almost everything in JavaScript (and TypeScript) is considered an object.*
Let's dive straight into the answers with some clear examples:
Object encompasses any non-null valueobject includes any non-primitive value{} is essentially the same as Object{ [k: string]: any } is similar to Record<string, any>Record<K, T> is a practical type for forming mapped types, commonly used instead of index signatures like Record<string, any> (as mentioned above). It can also specify precise key/value pairs such as Record<'foo' | 'bar', 'baz' | 'bang'>{ bar: "baz" | "bang"; foo: "baz" | "bang"; }Record<string, never>Record<string, unknown> or Record<string, any>unknown or anyTake into account the following regarding Object:
class C {}
const a: Object = 0
const b: Object = ""
const c: Object = []
const d: Object = {}
const e: Object = C
const f: Object = null // <-- error!
const g: Object = undefined // <-- error!
const h: Object = { foo: "bar" }
h.bar // Property 'foo' does not exist on type 'Object'.
Consider these points about object:
class C {}
const a: object = 0 // <-- error!
const b: object = "" // <-- error!
const c: object = []
const d: object = {}
const e: object = C
const f: object = undefined // <-- error!
const g: object = null // <-- error!
const h: object = { foo: "bar" }
h.bar // Property 'foo' does not exist on type 'object'.
Learn more about Record<K, T>.
Explore index signatures.
Dive into mapped types
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