TIPSCRIST: CAMINO HTMLELEMENTO

Question

¿Alguien sabe cómo lanzar en TypeScript?

Estoy tratando de hacer esto:

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

pero me da un error:

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

No puedo acceder al miembro 'Tipo' del elemento de script a menos que lo lleve al tipo correcto, pero no sé cómo hacerlo.Busqué en los docs y muestras, pero no pude encontrar nada.

Answer 1

Typycript usa '<>' para rodear los moldes, por lo que lo anterior se convierte en:

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

Sin embargo, desafortunadamente no puede hacer:

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

Usted obtiene el error

Cannot convert 'NodeList' to 'HTMLScriptElement[]'

pero puedes hacer:

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

Answer 2

AS OF TIPSIPT 0.9 El archivo lib.d.ts utiliza firmas de sobrecarga especializadas que devuelven los tipos correctos para llamadas a getElementsByTagName.

Esto significa que ya no necesita usar las afirmaciones de tipo para cambiar el tipo:

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

Answer 3

Siempre puede piratear el sistema de tipo usando:

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

Answer 4

No escriba el reparto.Nunca.Usa GUARDIES DE 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.

Deje que el compilador haga el trabajo para usted y obtenga errores cuando sus supuestos resultan mal.

Puede verse demasiado en este caso, pero le ayudará mucho si regresa más tarde y cambia el selector, como agregar una clase que falta en el DOM, por ejemplo.

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];