TypeScript Error with angular2 : string is not assignable

Question

I am creating a custom pipe in Angular2 while writing a code for filter I am getting following build error:

TS2322: Build:Type'() => string' is not assignable to type 'string'

Please find my sample code below:

import { PipeTransform, Pipe } from 'angular2/core';
import { IProduct } from './products';
@Pipe({
name: 'productFilter'
})


export class ProductFilterPipe implements PipeTransform {
 transform(value: IProduct[], args: string[]): IProduct[] {
    let filter: string = args[0].toLocaleLowerCase ?    args[0].toLocaleLowerCase : null;
    return filter ? value.filter((product: IProduct) =>
        product.productName.toLocaleLowerCase().indexOf(filter) != -1) :   value;
}
}

Above error comes in following line of code:

let filter:

I am new to typescript can someone help me with fixing this issue?

Answer 1

You need to add parentheses to the call of the function toLocaleLowerCase. In other words you should make it: toLocaleLowerCase()

Because you're not really callingbthe function when you provide its name without parantheses. You are saying that you want the variable filter to be equal to the function itself, not to the value returned from the function after calling it.