index signature in typescript

Index Signatures

read the code below.

interface Foo {
    [index: string]: number
}

let foo: Foo = { x: 1, y: 2 };
console.log(foo['x']); // number

interface Bar {
    [key: string]: number
}

let bar: Bar = { x: 1, y: 2 };
console.log(bar['x']); // number

interface Baz {
    [random_name: string]: number
}

let baz: Baz = { x: 1, y: 2 };
console.log(baz['x']); // number

[] indicates the index signature

all the three code snnippts are equal, since [] is the index signature and the name in it is unrelevent. this is similar to function signature where the name of the parameter does not matter.