How to get text of an input text box during onKeyP…

I am trying to get the text in a text box as the user types in it (jsfiddle playground):

function edValueKeyPress() {
    var edValue = document.getElementById("edValue");
    var s = edValue.value;

    var lblValue = document.getElementById("lblValue");
    lblValue.innerText = "The text box contains: " + s;

    //var s = $("#edValue").val();
    //$("#lblValue").text(s);    
}

<input id="edValue" type="text" onKeyPress="edValueKeyPress()"><br>
<span id="lblValue">The text box contains: </span>

The code runs without errors, except that the value of the input text box, during onKeyPress is always the value before the change:

enter image description here

Question: How do I get the text of a text box during onKeyPress?

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There are three events related to “the user is typing” in the HTML DOM:

onKeyDown
onKeyPress
onKeyUp

In Windows, the order of WM_Key messages becomes important when the user holds down a key, and the key begins to repeat:

WM_KEYDOWN('a') – user has pushed down the A key
WM_CHAR('a') – an a character has been received from the user
WM_CHAR('a') – an a character has been received from the user
WM_CHAR('a') – an a character has been received from the user
WM_CHAR('a') – an a character has been received from the user
WM_CHAR('a') – an a character has been received from the user
WM_KEYUP('a') – the user has released the A key

Will result in five characters appearing in a text control: aaaaa

The important point being that the you respond to the WM_CHAR message, the one that repeats. Otherwise you miss events when a key is pressed.

In HTML things are slightly different:

onKeyDown
onKeyPress
onKeyDown
onKeyPress
onKeyDown
onKeyPress
onKeyDown
onKeyPress
onKeyDown
onKeyPress
onKeyUp

Html delivers an KeyDown and KeyPress every key repeat. And the KeyUp event is only raised when the user releases the key.

Take aways

I can respond to onKeyDown or onKeyPress, but both are still raised before the input.value has been updated
I cannot respond to onKeyUp, because it doesn’t happen as the text in the text-box changes.

Question: How do I get the text of a text-box during onKeyPress?

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Answer

Handling the input event is a consistent solution: it is supported for textarea and input elements in all contemporary browsers and it fires exactly when you need it:

function edValueKeyPress() {
    var edValue = document.getElementById("edValue");
    var s = edValue.value;

    var lblValue = document.getElementById("lblValue");
    lblValue.innerText = "The text box contains: " + s;
}

<input id="edValue" type="text" onInput="edValueKeyPress()"><br>
<span id="lblValue">The text box contains: </span>

I’d rewrite this a bit, though:

function showCurrentValue(event)
{
    const value = event.target.value;
    document.getElementById("label").innerText = value;
}

<input type="text" onInput="showCurrentValue(event)"><br>
The text box contains: <span id="label"></span>

How to get text of an input text box during onKeyPress?

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