Destinazione: colata htmlelement

Question

Qualcuno sa come lanciare i dattilvi?

Sto cercando di fare questo:

var script:HTMLScriptElement = document.getElementsByName("script")[0];
alert(script.type);

.

Ma mi sta dando un errore:

Cannot convert 'Node' to 'HTMLScriptElement': Type 'Node' is missing property 'defer' from type 'HTMLScriptElement'
(elementName: string) => NodeList

.

Non riesco ad accedere al membro del "tipo" dell'elemento di script, a meno che non lo gettassi al tipo corretto, ma non so come farlo.Ho cercato i documenti e i campioni, ma non ho trovato nulla.

Answer 1

dattilografo utilizza '<>' per surround cast, quindi quanto sopra diventa:

var script = <HTMLScriptElement>document.getElementsByName("script")[0];

.

Tuttavia, purtroppo non puoi fare:

var script = (<HTMLScriptElement[]>document.getElementsByName(id))[0];

.

Ottieni l'errore

Cannot convert 'NodeList' to 'HTMLScriptElement[]'

.

Ma puoi fare:

(<HTMLScriptElement[]><any>document.getElementsByName(id))[0];

.

Answer 2

AS di DESTRISTRICT 0.9 Il file lib.d.ts utilizza firme di sovraccarico specializzate che restituiscono i tipi corretti per le chiamate a getElementsByTagName.

Ciò significa che non è più necessario utilizzare le asserzioni di tipo per modificare il tipo:

// No type assertions needed
var script: HTMLScriptElement = document.getElementsByTagName('script')[0];
alert(script.type);

.

Answer 3

Puoi sempre hackerare il sistema di tipo usando:

var script = (<HTMLScriptElement[]><any>document.getElementsByName(id))[0];

.

Answer 4

Non digitare il cast.Mai.Utilizzare Guardie di tipo:

const e = document.getElementsByName("script")[0];
if (!(e instanceof HTMLScriptElement)) 
  throw new Error(`Expected e to be an HTMLScriptElement, was ${e && e.constructor && e.constructor.name || e}`);
// locally TypeScript now types e as an HTMLScriptElement, same as if you casted it.

.

Lascia che il compilatore faccia il lavoro per te e ottenere errori quando le tue ipotesi risultano sbagliate.

Può sembrare eccessivamente in questo caso, ma ti aiuterà molto se torni più tardi e cambierà il selettore, come aggiungere una classe che manca nel DOM, ad esempio.

Answer 5

To end up with:

• an actual Array object (not a NodeList dressed up as an Array)
• a list that is guaranteed to only include HTMLElements, not Nodes force-casted to HTMLElements
• a warm fuzzy feeling to do The Right Thing

Try this:

let nodeList : NodeList = document.getElementsByTagName('script');
let elementList : Array<HTMLElement> = [];

if (nodeList) {
    for (let i = 0; i < nodeList.length; i++) {
        let node : Node = nodeList[i];

        // Make sure it's really an Element
        if (node.nodeType == Node.ELEMENT_NODE) {
            elementList.push(node as HTMLElement);
        }
    }
}

Enjoy.

Answer 6

Just to clarify, this is correct.

Cannot convert 'NodeList' to 'HTMLScriptElement[]'

as a NodeList is not an actual array (e.g. it doesn't contain .forEach, .slice, .push, etc...).

Thus if it did convert to HTMLScriptElement[] in the type system, you'd get no type errors if you tried to call Array.prototype members on it at compile time, but it would fail at run time.

Answer 7

Updated example:

const script: HTMLScriptElement = document.getElementsByName(id).item(0) as HTMLScriptElement;

Documentation:

TypeScript - Basic Types - Type assertions

Answer 8

This seems to solve the problem, using the [index: TYPE] array access type, cheers.

interface ScriptNodeList extends NodeList {
    [index: number]: HTMLScriptElement;
}

var script = ( <ScriptNodeList>document.getElementsByName('foo') )[0];

Answer 9

Could be solved in the declaration file (lib.d.ts) if TypeScript would define HTMLCollection instead of NodeList as a return type.

DOM4 also specifies this as the correct return type, but older DOM specifications are less clear.

See also http://typescript.codeplex.com/workitem/252

Answer 10

Since it's a NodeList, not an Array, you shouldn't really be using brackets or casting to Array. The property way to get the first node is:

document.getElementsByName(id).item(0)

You can just cast that:

var script = <HTMLScriptElement> document.getElementsByName(id).item(0)

Or, extend NodeList:

interface HTMLScriptElementNodeList extends NodeList
{
    item(index: number): HTMLScriptElement;
}
var scripts = <HTMLScriptElementNodeList> document.getElementsByName('script'),
    script = scripts.item(0);

Answer 11

I would also recommend the sitepen guides

https://www.sitepen.com/blog/2013/12/31/definitive-guide-to-typescript/ (see below) and https://www.sitepen.com/blog/2014/08/22/advanced-typescript-concepts-classes-types/

TypeScript also allows you to specify different return types when an exact string is provided as an argument to a function. For example, TypeScript’s ambient declaration for the DOM’s createElement method looks like this:

createElement(tagName: 'a'): HTMLAnchorElement;
createElement(tagName: 'abbr'): HTMLElement;
createElement(tagName: 'address'): HTMLElement;
createElement(tagName: 'area'): HTMLAreaElement;
// ... etc.
createElement(tagName: string): HTMLElement;

This means, in TypeScript, when you call e.g. document.createElement('video'), TypeScript knows the return value is an HTMLVideoElement and will be able to ensure you are interacting correctly with the DOM Video API without any need to type assert.

Answer 12

var script = (<HTMLScriptElement[]><any>document.getElementsByName(id))[0];