Array VS Type[] in Typescript

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There isn’t any semantic difference

There is no difference at all. Type[] is the shorthand syntax for an array of Type. Array<Type> is the generic syntax. They are completely equivalent.

The handbook provides an example here. It is equivalent to write:

function loggingIdentity<T>(arg: T[]): T[] {
    console.log(arg.length);
    return arg;
}

Or:

function loggingIdentity<T>(arg: Array<T>): Array<T> {
    console.log(arg.length);
    return arg;
}

And here is a quote from some release notes:

Specifically, number[] is a shorthand version of Array<number>, just as Date[] is a shorthand for Array<Date>.

About the readonly type modifier

TypeScript 3.4, introduces the readonly type modifier. With a precision:

the readonly type modifier can only be used for syntax on array types and tuple types

let err2: readonly Array<boolean>; // error!    
let okay: readonly boolean[]; // works fine

The following declaration is equivalent to readonly boolean[]:

let okay2: ReadonlyArray<boolean>;

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