Make a text field accepts only digits

make-text-field-accepts-only-digits.js

$(function() {
    // Remove any character or symbole and keep only
    // numbers in the "Reference Number" input field
    $("input[type=text]").on("keyup keydown", function() {
        var refNumber = keepOnlyNumbers($(this).val());
        $(this).val(refNumber);
    });  
});

// Remove any character or symbol withen
// the provided value and keep only numbers
function keepOnlyNumbers(value) {
    if (value.length === 0) {
        return "";
    }

    var items = value.split("");
    var filteredItems = [];

    items.forEach(function(val, index){
        // If val is a number
        if (! isNaN(parseInt(val.trim()))) {
            filteredItems.push(val);
        }
    });

    return filteredItems.join("");
}