Use class variable in filter method

Question

I am using AngularJS and Typescript. The problem I am trying to solve is the following:

In the Typescript controller class I have an array of loans, each loan with a currency object.
In the UI I have one tab per currency.

I want to call a getLoans() method to show the loan list within each tab (currency). In the class, I have an array with all the loans and the getLoans() method filters that array based on the selected tab (selected currency) and returns the loans filtered.

Below is the code:

class MyClass {
    public selectedCurrency: app.models.Currency;
    private loans: app.models.Loan[];

    getLoans(): app.models.Loan[] {
        if (this.loans) {
            return this.loans.filter(this.filterBySelectedCurrency);
        }
        return null;
    }

    filterBySelectedCurrency(loan: app.models.Loan): boolean {
        return loan && this.selectedCurrency && loan.Currency == this.selectedCurrency;
    }
}

The above code is not working because in the filterBySelectedCurrency(..) method this.selectedCurrency is undefined. However, debugging the code I see that before calling it (within the getLoans() method), this.selectedCurrency has the correct value.

Apparently for some reason, I can't access the class variable this.selectedCurrency from within the filter method. Is this the case?

Thanks in advance!

David Sherret · Accepted Answer · 2016-06-27 15:20:43Z

2

Passing in the function directly will cause the context—this—to be lost. You can maintain the context by passing in an arrow function instead.

Change this:

return this.loans.filter(this.filterBySelectedCurrency);

To this:

return this.loans.filter((loan) => this.filterBySelectedCurrency(loan));

answered Jun 27, 2016 at 15:20

David Sherret

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