Input mask number on pure js

script.js

function mask(event, selector) {
    var keyCode;

    var input = document.querySelector(selector);

    function maskInput(event) {
        event.keyCode && (keyCode = event.keyCode);
        var pos = this.selectionStart;
        if (pos < 3) event.preventDefault();

        var matrix = "+0 (___) ___ __ __",
            i = 0,
            def = matrix.replace(/\D/g, ""),
            val = this.value.replace(/\D/g, ""),
            new_value = matrix.replace(/[_\d]/g, function (a) {
                return i < val.length ? val.charAt(i++) || def.charAt(i) : a
            });
        i = new_value.indexOf("_");
        if (i != -1) {
            i < 5 && (i = 3);
            new_value = new_value.slice(0, i)
        }
        var reg = matrix.substr(0, this.value.length).replace(/_+/g,
            function (a) {
                return "\\d{1," + a.length + "}"
            }).replace(/[+()]/g, "\\$&");
        reg = new RegExp("^" + reg + "$");
        if (!reg.test(this.value) || this.value.length < 5 || keyCode > 47 && keyCode < 58) this.value = new_value;
        if (event.type == "blur" && this.value.length < 5) this.value = "";

    }


    if (input) {
        input.addEventListener("input", maskInput, false);
        input.addEventListener("focus", maskInput, false);
        input.addEventListener("blur", maskInput, false);
        input.addEventListener("keydown", maskInput, false)
    }
}