Concatenate with Null Undefined not Working in Angular Typescript

Question

I am trying to concatenate words and at same time, remove, null and undefined. Currently still getting error in the image below. How would someone resolve this?

javascript-string-concatenation-behavior-with-null-or-undefined-values

In the picture, one of the properties is saying

TypeError: cannot read property of undefined

Its like it cannot even read the argument in first place, to apply the undefined filters, etc.

get copyFromDescription() {
    if (this.addressId == 0) {
        return 'Select';
    } else { return [this.apn, this.combinedAddress,this.addressType.addressTypeDescription].filter(Boolean).join('') }
}

Data Value Picture

Adrian Brand · Accepted Answer · 2019-12-03 06:42:41Z

1

Use

.filter(val => !!val)

Boolean is a type

and test for addressType being undefined with

this.addressType && this.addressType.addressTypeDescription

get copyFromDescription() {
    if (this.addressId == 0) {
        return 'Select';
    } else { return [this.apn, this.combinedAddress,this.addressType && this.addressType.addressTypeDescription].filter(val => !!val).join('') }
}

edited Dec 3, 2019 at 6:42

answered Dec 3, 2019 at 6:39

Adrian Brand

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2 Comments

user12425844 Over a year ago

also placed a comment, for some reason in my data model, address Type exists, but did not get into the new object array, strange, I will try this out also

user12425844 Over a year ago

also, addessType is nullable member in my model, so when I initialized the model, without that member, its not even showing, thanks

Hobbes · Accepted Answer · 2019-12-03 06:52:14Z

this.addressType is undefined. Therefore it can't get a value when trying to access the addressTypeDescription property.

Boolean is a type and not a test. This seems a bit more logical to me.

get copyFromDescription() {
    if (this.addressId == 0) {
        return 'Select';
    } else { return [this.apn, this.combinedAddress,this.addressType.addressTypeDescription].filter(val => !!val).join('') }
}

but then you will still be stuck with the undefined error which needs to be tested for.

get copyFromDescription() {
    if (this.addressId === 0) 
        return 'Select';
    else if (this.addressType) return [this.apn, this.combinedAddress, this.addressType.addressTypeDescription]
      .filter(val => !!val).join('');
    else return [this.apn, this.combinedAddress] // you cannot use addressType here
      .filter(val => !!val).join('');
}

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