尝试编写一些干净的JS排序函数。下面是我的模板中一个按钮的click处理程序，它调用各个方法按不同的属性排序。

（click）=“addresses.sort（sortByTown）”

它调用下面的方法。它的工作很好，这是很好的！

sortByTown(address1: any, address2: any): number {
    const a = address1.town.toUpperCase();
    const b = address2.town.toUpperCase();
    if (a > b) {
      return 1;
    } else if (a < b) {
      return -1;
    }
    return 0;
  }

我遇到的问题是，我已经有了大约4个这样的排序方法，我想把if语句放入它们自己的函数中，以便更好地编写干巴巴的代码。所以我尝试了下面的方法，但是compareFunction甚至从来没有调用过GET。我做错了什么？

sortByTown(address1: any, address2: any): number {
    const a = address1.town.toUpperCase();
    const b = address2.town.toUpperCase();
    return this.compareAddresses(a, b);
  }

  compareAddresses(a: string | number, b: string | number): number {
    if (a > b) {
      return 1;
    } else if (a < b) {
      return -1;
    }
    return 0;
  }

TypeError: Cannot read property 'compareAddresses' of undefined
    at sortByStreetName (address.component.ts:43)
    at Array.sort (<anonymous>)
    at AddressComponent_Template_button_click_9_listener (address.component.html:10)
    at executeListenerWithErrorHandling (core.js:15182)
    at wrapListenerIn_markDirtyAndPreventDefault (core.js:15217)
    at HTMLButtonElement.<anonymous> (platform-browser.js:582)
    at ZoneDelegate.invokeTask (zone-evergreen.js:406)
    at Object.onInvokeTask (core.js:28500)
    at ZoneDelegate.invokeTask (zone-evergreen.js:405)
    at Zone.runTask (zone-evergreen.js:178)