Why does the TypeScript type checker allow this code snippet to pass? Is there a way I can increase its strictness?
const foo: {} = {bar: 123}
Why does the TypeScript type checker allow this code snippet to pass? Is there a way I can increase its strictness?
const foo: {} = {bar: 123}
The issue was resolved by specifying the type as Record<any, never>.
const foo: Record<any,never> = {} // successfully compiles
const bar: Record<any,never> = {bar: 123} // error occurs as anticipated
The object type covers a wide range of possibilities. It can be either empty or contain properties.
If you want to validate object properties, it's advisable to use the null type instead of an empty object and define a specific type or interface for it.
Take a look at this TypeScript playground example
interface Foo {
bar: number
}
var foo: Foo | null = null
foo = {
bar: 123
}
let x: { [key: string]: never } = {} // this is valid
let y: {[key : string]: never } = {a:1} // this will trigger an error
When assigning any object to {}, you may encounter a situation where the properties of the type are not available for use:
const foo: {} = {bar: 123}
foo.bar // error : Property 'bar' does not exist on type '{}'
To prevent this issue, it is recommended to define a type first or let the compiler infer the type during declaration:
// Defining a type (an interface can also be used)
type Foo = {
bar: number;
}
const foo: Foo = {bar: 123};
foo.bar // type: number
// Using type inference:
const foo = {bar: 123};
foo.bar // type: number
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