So for adding the validation we will copy this input box html on the page

    <div class="form-group row">
        <label for="inputPassword" class="col-sm-2 col-form-label">Paste remove some special character like "\"</label>
        <div class="col-sm-10">
            <input type="text" class="form-control" placeholder="Enter Value" name="removePaste" id="removePaste" value="" />
        </div>
    </div>

Now we have to register keypress event to stop backslash on user type. So adding the event will stop users from enter backslash.

     $('#removePaste').on('keypress', function(event) {
        let keyPressed = event.keyCode || event.which;
        if (keyPressed == 92) {
            event.preventDefault();
            return false;
        }
    });

So, even after we stop back slash on kepress user can still copy and paste the backslash in the textbox, so we have to make user to stop copy paste slash using copy/paster. For that purpose we will add another paste event  and then replace the back slashes from blank .

     $('#removePaste').on('paste', function(event) {
        event.preventDefault();
        blockPaste(event, this);
    });

You have to add this function in your script. This is replacing the back slashes with blanks and thus helps us to stop user from invalid character. 

So this is how to apply Input validation to stop backslash on keypress and copy paste.

    function blockPaste(event, element) {
        var pastedData = event.originalEvent.clipboardData.getData('text/plain');
        var newString = pastedData.replace(/\\/g, '');
        console.log(newString);
        element.value = element.value + newString;
    }