Why is Event target not Element in Typescript

Question

I simply want to do this with my KeyboardEvent  var tag   evt target tagName toLowerCase      While Event target is of type EventTarget it does not inherit from Element  So I have to cast it like this   var tag     lt Element gt evt target  tagName toLowerCase      This is probably due to some browsers not following standards  right  What is the correct browser agnostic implementation in TypeScript   PS  I am using jQuery to capture the KeyboardEvent

User · Answer

With typescript we can leverage type aliases  like so   type KeyboardEvent       target  HTMLInputElement    key  string     const onKeyPress    e  KeyboardEvent    gt      if   Enter      e key       Enter keyboard was pressed      submit e target value       e target value           return           continue handle onKeyPress input events

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Bangonkali provide the right answer  but this syntax seems more readable and just nicer to me   eventChange  event  KeyboardEvent   void         lt HTMLInputElement gt  event target  value

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Typescript 3 2 4  For retrieving property you must cast target to appropriate data type   e   gt  console log  e target as Element  id

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Using typescript  I use a custom interface that only applies to my function  Example use case     handleChange event    target  HTMLInputElement           this setState   value  event target value           In this case  the handleChange will receive an object with target field that is of type HTMLInputElement   Later in my code I can use    lt input type  text  value  this state value  onChange  this handleChange    gt    A cleaner approach would be to put the interface to a separate file    interface HandleNameChangeInterface     target  HTMLInputElement      then later use the following function definition     handleChange event  HandleNameChangeInterface        this setState   value  event target value           In my usecase  it s expressly defined that the only caller to handleChange is an HTML element type of input text

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I use this  onClick   target    MouseEvent    gt        const targetDivElement  HTMLDivElement   target as HTMLDivElement           const listFullHeight  number   targetDivElement scrollHeight      const listVisibleHeight  number   targetDivElement offsetHeight      const listTopScroll  number   targetDivElement scrollTop

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JLRishe s answer is correct  so I simply use this in my event handler   if  event target instanceof Element

User · Answer

It doesn t inherit from Element because not all event targets are elements   From MDN      Element  document  and window are the most common event targets  but other objects can be event targets too  for example XMLHttpRequest  AudioNode  AudioContext  and others    Even the KeyboardEvent you re trying to use can occur on a DOM element or on the window object  and theoretically on other things   so right there it wouldn t make sense for evt target to be defined as an Element   If it is an event on a DOM element  then I would say that you can safely assume evt target  is an Element  I don t think this is an matter of cross-browser behavior  Merely that EventTarget is a more abstract interface than Element   Further reading  https   typescript codeplex com discussions 432211

User · Answer

I m usually facing this problem when dealing with events from an input field  like key up  But remember that the event could stem from anywhere  e g  from a keyup listener on document  where there is no associated value  So in order to correctly provide the information I d provide an additional type  interface KeyboardEventOnInputField extends KeyboardEvent     target  HTMLInputElement           onKeyUp e  KeyboardEventOnInputField        const inputValue   e target value                If the input to the function has a type of Event  you might need to tell typescript what it actually is    onKeyUp e  Event        const evt   e as KeyboardEventOnInputField      const inputValue   evt target value      this inputValue next inputValue        This is for example required in Angular

User · Answer

Could you create your own generic interface that extends Event  Something like this   interface DOMEvent lt T extends EventTarget gt  extends Event     target  T     Then you can use it like   handleChange event  DOMEvent lt HTMLInputElement gt       this setState   value  event target value

[typescript] Why is Event.target not Element in Typescript?

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