Javascript 角度4，无法从函数的内部函数访问类的变量

我正在从firebase firestone获取数据，数据已成功检索并在控制台中打印。但我无法将数据保存到全局变量中此错误正好位于第37行

我想将数据保存到该变量，以便在ui中加载数据

24 thisaddress = {};
25  ngOnInit() {
26    this.data = new AddressserviceService();
27    this.sub = this.route.params.subscribe(params => {
28      this.id = params['id'];
29   });
30   
31   this.newvisitordb = AddressserviceService.getdb();
32   var docRef = this.newvisitordb.collection("addresses").doc(this.id);
33   docRef.get().then(function(doc) {
34        if (doc.exists) {
35          console.log("Document data:", doc.data());
36          //**this line is not working**
37          this.thisaddress= doc.data();
38        } 
39    }).catch(function(error) {
40        console.log("Error getting document:", error);
41    });

第37行出现错误

错误是

>     Error getting document: TypeError: Cannot set property 'thisaddress' of undefined
>         at eval (newvisitor.component.ts:45)
>         at ZoneDelegate.invoke (zone.js:388)
>         at Object.onInvoke (core.js:4733)
>         at ZoneDelegate.invoke (zone.js:387)
>         at Zone.run (zone.js:138)
>         at eval (zone.js:858)
>         at ZoneDelegate.invokeTask (zone.js:421)
>         at Object.onInvokeTask (core.js:4724)
>         at ZoneDelegate.invokeTask (zone.js:420)
>         at Zone.runTask (zone.js:188)

尝试改变

docRef.get().then(function(doc) {

到

尝试改变

docRef.get().then(function(doc) {

到

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这个问题已经回答了。