Javascript 使用typescript单击时删除画布元素

我是typescript新手，我正在尝试的是从div中删除canvas元素

<div class="chart">
    <canvas id="nav-chart"></canvas>
</div>

尝试此操作时，它会在以下行抛出错误：const elem:HTMLElement=document.getElementById（'nav-chart'）

TS2322: Type 'HTMLElement | null' is not assignable to type 'HTMLElement'.
  Type 'null' is not assignable to type 'HTMLElement'.

const elem: HTMLElement | null = document.getElementById('nav-chart')

在这行

elem.parentElement.removeChild（elem）

---

我首先找到了解决方案，我们必须用

HTMLElement|null

TS2322: Type 'HTMLElement | null' is not assignable to type 'HTMLElement'.
  Type 'null' is not assignable to type 'HTMLElement'.

const elem: HTMLElement | null = document.getElementById('nav-chart')

而且在条件之内

if (elem) {
      elem.parentElement && elem.parentElement.removeChild(elem)
}