vue.js:597 [Vue warn]: Error in callback for watcher "dat": "TypeError: Cannot read property 'call'

vue.js:597 [Vue warn]: Error in callback for watcher "dat": "TypeError: Cannot read property 'call' of undefined"

 

watch listener  

The mode attribute is wrong,

                dat:{
                    deep:true,
                    hander:function (newV, oldV) {
                        console.log(newV[0].name)
                    }
                },

The hander is wrong, it should be the handler

There is an error, the format is wrong, go to the official website to check