Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat’)” 錯誤原因: let arr = a.concat(b); 這句代碼中,a不能為undefined,傳資料出錯了。 Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat‘)“報錯Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat’)”