js获取输入框的值为什么一直是undefined

Question

js代码

mounted() {

        let val = [];
        let str = "";
        let ipt = document.getElementById('ipt');
        ipt.addEventListener('keyup',function () {
            val.push(ipt.value);
            if(val.length){
                    if(val.length >= str.length) {
                    str += val;
                }else {
                    str = str.substr(0, val.length)
                }
                this.value = val.replace(/./g, '*')
            }
        }, false)
        
    },

Answer 1

用vue为什么不用双向数据绑定呢？
还有你监听的keyup方法是否已触发？你的赋值是在这个方法触发后