普通函数与事件处理函数的区别?

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普通函数与事件处理函数的区别?What is the difference between ordinary functions and event handling functions?

composeUrl: function (str) { return  "../" + str + "/" + str },  tap: evt => {    // console.log(evt)    var pageUrl = composeUrl(evt.currentTarget.dataset.url)    // console.log(pageUrl)    wx.navigateTo({      url: pageUrl,    })}ReferenceError: composeUrl is not defined

Why is it invalid to define ordinary functions in page () (or it is impossible to define functions?), while event handling functions and life cycle functions are effective? What is the essential difference between them? Composeurl: function (STR) {return "/" + STR + "/" + STR},   tap: evt => {    //  console.log (evt)    var pageUrl = composeUrl( evt.currentTarget.dataset .url)    //  console.log (pageUrl)     wx.navigateTo ({      url: pageUrl,    })}ReferenceError: composeUrl is not defined

回答：

var pageUrl = this.composeUrl()