findIndex Array method in TypeScript

Question

I'm very new to Angular 4 development. I encounter someArray.findIndex() is not a function. How to add this .findIndex() javascript function in TypeScript.

I'm building a calendar component, following function gives me error

WEBPACK_IMPORTED_MODULE_2_lodash .findIndex is not a function at CalendarComponent.isSelected (calendar.component.ts:4

isSelected(date: moment.Moment): boolean {
    return _.findIndex(this.selectedDates, (selectedDate) => {
      return moment(date).isSame(selectedDate.mDate, 'day');
    }) > -1;
  }

Thank you so much.

Answer 1

It's not about Typescript. Javascript functions are included in Typescript. You are trying to use Lodash function. Make sure that you installed and imported it on top of the file:

import _ from 'lodash';

or just use Javascript function:

isSelected(date: moment.Moment): boolean {
    return this.selectedDates.findIndex((selectedDate) => {
      return moment(date).isSame(selectedDate.mDate, 'day');
    });
}

Answer 2

You are calling findIndex method of _. You are either using UnderscoreJS or Lodash .

As the error says WEBPACK_IMPORTED_MODULE_2_lodash.findIndex is not a function It means you are using lodash.

Import lodash library and it will work.

import _ from 'lodash';

Answer 3

selectedDate = arrayName.find(item => item.date === searchingdate);

Answer 4

you can use indexOf

[1,2,3,4,5].indexOf(1) //return 0
[1,2,3,4,5].indexOf(5) //return 4
[1,2,3,4,5].indexOf(6) //return -1
[1,2,3,4,5].indexOf(0) //return -1