Why Does the HTML Input With Type "Number" Allow the Letter 'E' to Be Entered in the Field

var ageInput = document.getElementById("age")

ageInput.addEventListener("keydown", function(e) {
  // prevent: "e", "=", ",", "-", "."
  if ([69, 187, 188, 189, 190].includes(e.keyCode)) {
    e.preventDefault();
  }
})

<input type="number" id="age">

HTML text input allow only numeric input

^{Note: This is an updated answer. Comments below refer to an old version which messed around with keycodes.}

JavaScript

Try it yourself on JSFiddle.

You can filter the input values of a text <input> with the following setInputFilter function (supports Copy+Paste, Drag+Drop, keyboard shortcuts, context menu operations, non-typeable keys, the caret position, different keyboard layouts, validity error message, and all browsers since IE 9):

// Restricts input for the given textbox to the given inputFilter function.
function setInputFilter(textbox, inputFilter, errMsg) {
  ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop", "focusout"].forEach(function(event) {
    textbox.addEventListener(event, function(e) {
      if (inputFilter(this.value)) {
        // Accepted value
        if (["keydown","mousedown","focusout"].indexOf(e.type) >= 0){
          this.classList.remove("input-error");
          this.setCustomValidity("");
        }
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty("oldValue")) {
        // Rejected value - restore the previous one
        this.classList.add("input-error");
        this.setCustomValidity(errMsg);
        this.reportValidity();
        this.value = this.oldValue;
        this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        // Rejected value - nothing to restore
        this.value = "";
      }
    });
  });
}

You can now use the setInputFilter function to install an input filter:

setInputFilter(document.getElementById("myTextBox"), function(value) {
  return /^\d*\.?\d*$/.test(value); // Allow digits and '.' only, using a RegExp
}, "Only digits and '.' are allowed");

Apply your preferred style to input-error class. Here's a suggestion:

.input-error{
  outline: 1px solid red;
}

See the JSFiddle demo for more input filter examples. Also note that you still must do server side validation!

TypeScript

Here is a TypeScript version of this.

function setInputFilter(textbox: Element, inputFilter: (value: string) => boolean, errMsg: string): void {
    ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop", "focusout"].forEach(function(event) {
        textbox.addEventListener(event, function(this: (HTMLInputElement | HTMLTextAreaElement) & {oldValue: string; oldSelectionStart: number | null, oldSelectionEnd: number | null}) {
            if (inputFilter(this.value)) {
                this.oldValue = this.value;
                this.oldSelectionStart = this.selectionStart;
                this.oldSelectionEnd = this.selectionEnd;
            } else if (Object.prototype.hasOwnProperty.call(this, 'oldValue')) {
                this.value = this.oldValue;
                if (this.oldSelectionStart !== null &&
                    this.oldSelectionEnd !== null) {
                    this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
                }
            } else {
                this.value = "";
            }
        });
    });
}

jQuery

There is also a jQuery version of this. See this answer.

HTML 5

HTML 5 has a native solution with <input type="number"> (see the specification), but note that browser support varies:

• Most browsers will only validate the input when submitting the form, and not when typing.
• Most mobile browsers don't support the step, min and max attributes.
• Chrome (version 71.0.3578.98) still allows the user to enter the characters e and E into the field. Also see this question.
• Firefox (version 64.0) and Edge (EdgeHTML version 17.17134) still allow the user to enter any text into the field.

Try it yourself on w3schools.com.

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