JS Array findIndex() is not a function

Question

The following code produces always an error:

var index = this.dataSource.findIndex(item => item.id_system === row.id_system);

The error message is: TypeError: this.dataSource.findIndex is not a function

What could be the solution?

null.findIndex, undefined.findIndex, {...}.findIndex, you need to have an array on findIndex, check the value of dataSource by console logging it — EugenSunic
– EugenSunic, Commented Jul 17, 2020 at 9:25
The solution is to make sure that this.dataSource is something that has a findIndex() function. Probably an array is what you're expecting. — Robby Cornelissen
– Robby Cornelissen, Commented Jul 17, 2020 at 9:27
[ {position: 1, name: 'Hydrogen', weight: 1.0079, symbol: 'H'}, {position: 2, name: 'Helium', weight: 4.0026, symbol: 'He'}, {position: 3, name: 'Lithium', weight: 6.941, symbol: 'Li'}, {position: 4, name: 'Beryllium', weight: 9.0122, symbol: 'Be'}, {position: 5, name: 'Boron', weight: 10.811, symbol: 'B'}, ]; — benni0108
– benni0108, Commented Jul 17, 2020 at 9:28

Emilien · Accepted Answer · 2020-07-17 09:32:56Z

2

If you're using Angular Material example, then you will need to use data array.

Your dataSource should be MatTableDataSource<your type>.

So maybe you can try

let index = this.dataSource.data.findIndex(item => item.id_system === row.id_system);

answered Jul 17, 2020 at 9:32

Emilien

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