实现一个只能输入数字的input框

// html部分
    <input id="numberInput" type="text" />

// js部分
    var inputEl = document.getElementById('numberInput');
    // var events =  ['input', 'keydown', 'keyup', 'select'];
    var events =  ['input'];
    events.forEach(function(event) {
        inputEl.addEventListener(event, function() {
            if (inputFilter(this.value)) {
                this.oldValue = this.value;
            } else if (this.hasOwnProperty('oldValue')) {
                this.value = this.oldValue;
            } else {
                this.value = '';
            }
        });
    });
    var numberReg = /^\d{0,6}$/;
    var inputFilter = function(val) {
        var isMatch = numberReg.test(val);
        if (isMatch) {
            return true;
        }
        return false;
    }