Add checkbox validation and error messaging for required options

src/App.vue

@@ -127,6 +127,16 @@ export default {
           type: 'error',
         });
         return;
+      } else if (item.type === 'checkbox' && item.required) {
+        this.itemStatus.answer = this.itemStatus.answer === undefined ? [] : this.itemStatus.answer;
+        const { minOpts, maxOpts } = Object.assign({ minOpts: 1, maxOpts: item.optTexts.length }, item);
+        if (this.itemStatus.answer.length < minOpts || this.itemStatus.answer.length > maxOpts) {
+          ElMessage({
+            message: sprintf(lang[this.settings.lang].checkboxOutOfRange, minOpts, maxOpts),
+            type: 'error',
+          });
+          return;
+        }
       }
 
       item.answer = this.itemStatus.answer;

src/lang.js

@@ -6,6 +6,7 @@ export default {
         'loading': 'Loading...',
         'input': 'Please input',
         'required': 'This field is required',
+        'checkboxOutOfRange': 'Please select at least %d and at most %d option(s)',
     },
     'zh-CN': {
         'submit': '提交',
@@ -14,5 +15,6 @@ export default {
         'loading': '加载中...',
         'input': '请输入',
         'required': '此字段不能为空',
+        'checkboxOutOfRange': '请选择 %d 到 %d 个选项',
     },
 }