Declare TypedArray with ArrayLike?

Question

I was looking for a way to declare generic TypedArray types in a d.ts file. TypedArray doesn't seem to exist for some reason but I came across a comment somewhere that suggested using ArrayLike<T>. Would this still be the best solution?

I can make a guess at what ArrayLike is, but is there any documentation for it? Googling and searching the Typescript site doesn't turn up much.

EDIT: I just noticed that typed array constructors are declared to take an ArrayLike as the first parameter, so that would indicate this is the right way to go.

MartyIX · Accepted Answer · 2015-10-26 20:56:58Z

5

I'm not sure if I understand your question correctly but the following instantiations work in TypeScript 1.6 (the latest stable version at the time of writing):

let t01 = new Uint8Array([1, 2, 3, 4]);
let t02 = new Int8Array([1, 2, 3, 4]);  
let t03 = new Uint8Array([1, 2, 3, 4]);
let t04 = new Uint8ClampedArray([1, 2, 3, 4]);
let t05 = new Int16Array([1, 2, 3, 4]);
let t06 = new Uint16Array([1, 2, 3, 4]);
let t07 = new Int32Array([1, 2, 3, 4]);
let t08 = new Uint32Array([1, 2, 3, 4]);
let t09 = new Float32Array([1.5, 2.5, 3.5, 4.5]);
let t10 = new Float64Array([1.5, 2.5, 3.5, 4.5]);

let arrayBuffer = new ArrayBuffer(16);

(TypeScript playground with the previous script, MDN documentation)

You can see that typed arrays are in es6.d.ts file:

/**
  * A typed array of 8-bit integer values. The contents are initialized to 0. If the requested 
  * number of bytes could not be allocated an exception is raised.
  */
interface Int8Array {
    /** 
      * Returns an array of key, value pairs for every entry in the array
      */
    entries(): IterableIterator<[number, number]>;
    /** 
      * Returns an list of keys in the array
      */
    keys(): IterableIterator<number>;
    /** 
      * Returns an list of values in the array
      */
    values(): IterableIterator<number>;
    [Symbol.iterator](): IterableIterator<number>;
}

Is this what you are after?

EDIT:

lib.es6.d.ts defines ArrayLike (see definition of what is Array-like in JavaScript) as:

interface ArrayLike<T> {
    length: number;
    [n: number]: T;
}

and Iterable as

interface Iterable<T> {
    [Symbol.iterator](): Iterator<T>;
}

This is how a function very similar to yours is defined:

interface Uint8ArrayConstructor {

    //
    // ...
    // 

    /**
      * Creates an array from an array-like or iterable object.
      * @param arrayLike An array-like or iterable object to convert to an array.
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
    from(arrayLike: ArrayLike<number> | Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Uint8Array;
}

so I would define your function as:

function foo(arrayLike: ArrayLike<number> | Iterable<number>) { ... }

edited Oct 26, 2015 at 20:56

answered Oct 26, 2015 at 15:39

MartyIX

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2 Comments

pixelmike Over a year ago

Thanks. I was looking to write a function to take a TypedArray or Array parameter. Eg: function foo(a:ArrayLike<number>) {.... It looks like I should be using Iterable<number>. But using Atom, if I hover over new Float32Array(a) it says the constructor takes ArrayLike<number>.

MartyIX Over a year ago

I edited my answer. Maybe it helps you understand more.

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