[bug report] alert written in the change event of El input number component cannot be closed

### Element UI version
2.15.0

### OS/Browsers version
win10

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/payneffff/pen/MWbYXdQ

### Steps to reproduce
在el-input-number组件的change事件中写alert，会一直触发组件的增加事件

### What is Expected?
能够正常关闭alert

### What is actually happening?
无法关闭alert