如何通过占位符在Protractor中定位元素。我试过$（＆＃39; [占位符=文章名称]＆＃39;）。click（）;
它显示错误＆＃34;失败：选择器无效：指定了无效或非法的选择器＆＃34;`
<input _ngcontent-c30="" class="mat-input-element mat-form-field-autofill-control ng-pristine ng-invalid ng-touched" matinput="" required="" maxlength="80" pattern="[A-Za-z0-9 ]{1,80}" id="mat-input-51" placeholder="Article name" aria-invalid="true" aria-required="true" aria-describedby="mat-error-0">
`