how to delete the character typed in key press event

Question

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I want to delete the character typed in the text box if it is not a number or decimal point in key press event. but I can not do this in the code that handle key press event because the character is displayed after key press event. please tell me how can I do this ?
when a character is typed, if it is other than number, I want to delete it, because if it is not deleted, if user does not delete it, that will lead to incorrect data.
I want to display only numbers and one decimal point. if user types any other character it should not displayed in the textbox.

JavaScript

span = document.createElement("span");
var txt1=($('<input>').attr('type', 'text').attr('id', 'id1').appendTo(span));
txt1.bind("keypress", function () {
    if (!validatedText(txt1.attr('id'), event)){
         removeCharEntered(txt1.attr('id'));
    }
});
var validatedText = function (id, event) {
var text=$('#' + id).val();
var len = text.length;
var ch = event.charCode;
//check for number
if (ch != 46) {
    if ((ch < 48) || (ch > 57)) {
        alert('please enter numbers only.');
        return false;
    }
}
//check for more than one decimal
else
    for (var i = 0; i < len; i++) {
        if (text.charAt(i) == '.'){
            alert('please enter numbers only.');
            return false;
        }
    }
return true;
};
//remove if character is not a number and decimal 
var removeCharEntered = function (id) {
var text = $('#' + id).val();
var len = text.length;
$('#' + id).val(text.substr(0,len - 1));
}

Posted 20-Jan-16 2:48am

Member 7854207

Updated 20-Jan-16 3:09am

v3

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Comments

John C Rayan 20-Jan-16 11:35am

Have a look at REGEX.

Sergey Alexandrovich Kryukov 20-Jan-16 12:35pm

This is the inquirer's problem. Please see my comment below and Solution 1.
—SA

Sergey Alexandrovich Kryukov 20-Jan-16 12:34pm

You don't need to "delete" it. You can filter out key presses so certain characters won't even appear.
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2016-01-20T06:48:00

Please see my comment to the question. Deleting wrong character is not a valid option. Instead, you should filter out some unwanted characters, so they won't even appear in the input.

For this purpose, your event handler should have an additional argument (which you need anyway), the instance of the event object, let's say, its name is event. On certain condition, you want to block some character from input. This is done by calling the function event.preventDefault():
https://developer.mozilla.org/en-US/docs/Web/API/Event/preventDefault[^].

(See also: Event.defaultPrevented — Web APIs | MDN[^], Event.stopPropagation() — Web APIs | MDN[^].)

It does not matter if you do it using jQuery or not. Please see this jQuery help page: .keypress() | jQuery API Documentation[^].

On this page, please find the sample code fragment with event.preventDefault(); from this code sample, you will see how to use this technique with jQuery.

—SA