Cannot read property 'push' of undefined in empty array

Question

Trying to get rid of the error TypeError: Cannot read property 'push' of undefined. I have this snippet causing the issue:

const parent_lead_contact = this.props.parentLeads?.filter((lead) =>
      lead.contact_guid.includes(this.props.parent_lead_party_guid)
    );// This is an array which can be empty
    if (parent_lead_contact?.length > 0) {
      parent_lead_contact[0].is_parent_lead_contact = true;
    } else {
      parent_lead_contact.push({ is_parent_lead_contact: true }); //  TypeError: Cannot read property 'push' of undefined
    }

Is there a proper way to get this? I am filtering data from a selector. Sometimes, the result would be an empty array. The important thing is that the selector is not returning is_parent_lead_contact property, but I have to add this property to the array regardless the array is empty.

Thanks a lot for spotting the issue.

Sometimes, the result would be an empty array ... and sometimes it seems, this.props.parentLeads is undefined - otherwise, why would you use ?.filter rather than just .filter — Jaromanda X
– Jaromanda X, Commented Oct 26, 2022 at 0:45

CertainPerformance · Accepted Answer · 2022-10-26 00:45:48Z

1

If an optional chain fails, everything past the ?. is ignored, and the expression evaluates to undefined. So this line

const parent_lead_contact = this.props.parentLeads?.filter((lead) =>
      lead.contact_guid.includes(this.props.parent_lead_party_guid)
);// This is an array which can be empty

will not produce an array that might be empty - rather, it'll produce either an array that's been filtered, or undefined. That line should be changed to

const parent_lead_contact = this.props.parentLeads?.filter((lead) =>
      lead.contact_guid.includes(this.props.parent_lead_party_guid)
) ?? [];

answered Oct 26, 2022 at 0:45

CertainPerformance

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