I am dealing with an object that can have a type of WithBalance | WithoutBalance
withBalance : { balance:number, name:string } withoutBalance : { name : string}
<span>{{object?.balance ?? 0}} </span>
However, when I attempt to access the balance property, I encounter the error message:
Property 'balance' does not exist on type WithoutBalanceAny suggestions on how to resolve this issue?
When working with angular templates, it is beneficial to explore the concept of Type Narrowing. For detailed insights, refer to this helpful resource
In situations like these, consider either assigning a new property called type to the objects with the type's name as a string and implement a conditional check, or directly verify the object's property within the template as demonstrated in the aforementioned reference.
Approach 1
withBalance : { balance:number, name:string, type:"withBalance" } withoutBalance : { name : string, type:"withoutBalance"}
<span>{{object.type=="withBalance"? object.balance: 0}} </span>
Approach 2
getBalance (obj:any){
if ("balance" in obj) {
return obj.balance
}
return 0;
}
<span>
{{ getBalance(object)}}
</span>
When it comes to optional chaining (?.), TypeScript allows us to create code that can stop running certain expressions immediately upon encountering a null or undefined value. For instance, if you use object?.balance, it means that the code will try to access the balance property only if object is not null. If object belongs to the withoutBalance type, an error like this may occur:
Property 'balance' does not exist on type WithoutBalanceTo handle this situation in your component, you can utilize the in operator as shown below:
getBalance (){
if ("balance" in this.object) {
return this.object.balance
}
return 0;
}
<span>
{{ getBalance()}}
</span>
To achieve this functionality, follow these steps:
// Define the type in your data.model.ts file
export interface Account {
name: string;
balance?: number
}
// Instantiate the model with a balance
const accountWithBalance: Account = {
name: 'Account A',
balance: 50
}
// Create an account without a balance
const accountWithoutBalance: Account = {
name: 'Account B',
// The balance field is optional here
}
// Display the balance in your template
<span> {{accountWithoutBalance.balance == null ? accountWithoutBalance.balance : 0}} </span>
It's crucial to use == null instead of withoutBalance.balance??0 because TypeScript may convert numeric values like 0 or 1 into boolean types unintentionally. Using == null ensures that the condition is only true if the balance field is null or undefined.
Here's a solution:
<span>{{$any(item).balance ?? 0}} </span>
By using this code, you can suppress any potential errors. Make sure to use it only if you are confident in the accuracy of your model.
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