How to block +,-,e in input type Number?

You can block entering those chars with keydown event

var inputBox = document.getElementById("inputBox");

var invalidChars = [
  "-",
  "+",
  "e",
];

inputBox.addEventListener("keydown", function(e) {
  if (invalidChars.includes(e.key)) {
    e.preventDefault();
  }
});

<input type="number" id="inputBox" />

but the user can still enter them if s/he does a copy/paste (or through the console). To prevent copy/paste, you can do a replace on the entered value ^[*].

var inputBox = document.getElementById("inputBox");

var invalidChars = [
  "-",
  "+",
  "e",
];

inputBox.addEventListener("input", function() {
  this.value = this.value.replace(/[e\+\-]/gi, "");
});

inputBox.addEventListener("keydown", function(e) {
  if (invalidChars.includes(e.key)) {
    e.preventDefault();
  }
});

<input type="number" id="inputBox" />

* You can't really get the entered value on an input field with type set to number. You can get the entered value as long as it is a number, that is, the value passes the internal number check. If the user copy/paste 1e, suggested solution will fail.

What happens when you enter 1e is that, input field checks if it's a number, and if it's not (1e is not) it throws a warning:

The specified value "1e" is not a valid number. The value must match to the following regular expression: -?(\d+|\d+.\d+|.\d+)([eE][-+]?\d+)?

and the value property is set to "".

If you check the field's properties, you'll find valueAsNumber property. If the entered value is a number, input field parses the value and stores it in valueAsNumber. Since 1e is not a number, it evaluates to NaN, and NaN is assigned to valueAsNumber and value is set to "". Though you still see 1e on the input field.

I've asked a question related to this problem, but no solution yet.

Get the entered value on number input field, not the parsed

Try preventing the default behaviour if you don't like the incoming key value:

document.querySelector(".your_class").addEventListener("keypress", function (evt) {
    if (evt.which != 8 && evt.which != 0 && evt.which < 48 || evt.which > 57)
    {
        evt.preventDefault();
    }
});

// 0 for null values
// 8 for backspace 
// 48-57 for 0-9 numbers

<input type="number" class="your_class">