Typescript TypeError: Unable to call function this.array[i].greet as it is not defined

When attempting to call my function, I am encountering an error. Interestingly, everything works fine when I create just one object of someClass and then utilize the greet function.

This is what does not work (someArray being an array of type someClass):

for (let i = 0; i < this.someArray.length; i++) {

        this.someArray[i].greet();
}

However, the following code snippet does work:

let oneInstance: someClass = new someClass;
oneInstance.id = 'abc';
console.log(oneInstance.greet());

In this scenario, SomeArray represents an array of my class called someClass:

export class someClass implements ISomeClass {

    id: string;

    public greet() {
        return "Hello, " + this.id;
    }
}

Answer №1

One possible issue could be that when populating your array with data, you may not be creating new instances of your class but rather assigning objects that share the same structure.

Instead of instantiating your class properly, you might be simply doing:

this.someArray = json.results;

Where json.results looks like this:

[{
    id: "id1"
} ... {
    id: "idn"
}]

This approach will give you objects with an 'id' property, but they won't have access to the class methods because you haven't actually created instances of the class. To solve this, you should consider something along the lines of:

this.someArray = json.results.map(item => Object.assign(new someClass(), item));

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