<el-form :model="changePassword" ref="ruleForm" label-width="100px">
            <el-form-item label="新密码：" prop="password">
                <el-input
                    @input.native="onInput($event, 'newPassword')"
                    type="text"
                    v-model="newPassword"
                    maxlength="12"
                    placeholder="6-12位字符，支持数字、大小写英文" >
                </el-input>
            </el-form-item>
            <el-form-item label="重复新密码：" prop="repeatPassword">
                <el-input
                    @input.native="onInput($event, 'repeatPassword')"
                    type="text"
                    maxlength="12"
                    v-model="repeatPassword"
                    placeholder="再次输入登录密码">
                </el-input>
            </el-form-item>
        </el-form>

js代码

data () {
    return {
        verifyData: {},
        changePassword: {
            step: 1,
            type: 'message',
            tel: '',
            verifyCode: '',
            password: '',
            newPassword: '',
            repeatPassword: ''
        },
        password: '',
        newPassword: '',
        repeatPassword: ''
    }
},
  methods: {
    // 监听输入
    onInput (e, type) {
        if (e.data) {
            if (this.changePassword[type].length < 12) {
                this.changePassword[type] += e.data
                setTimeout(() => {
                    this[type] = this[type].replace(/./g, '*')
                }, 700)
            }
        } else {
            if (this.changePassword[type].length > 0) {
                this.changePassword[type] = this.changePassword[type].substring(0, this.changePassword[type].length - 1)
            }
        }
    }
   }

也可以使用下面这种

// 监听输入
onInput (e, type) {
    if (e.data) {
        if (this.changePassword[type].length < 12) {
            this.changePassword[type] += e.data
        }
    } else {
        if (this.changePassword[type].length > 0) {
            this.changePassword[type] = this.changePassword[type].substring(0, this.changePassword[type].length - 1)
        }
    }
},
onKeyUp (type) {
    this[type] = this[type].replace(/./g, '*')
},