Cannot invoke an object which is possible undefined'

Mark

Here is the property and method

private errorMessages = new Map string>();


public get errors(): Array {
    if (!this.control) {
        return [];
    }

    const { errors } = this.control;
    return Object.keys(errors).map(key => this.errorMessages.has(key) ? 
  this.errorMessages.get(key)() : errors[key] || key);
}

I get this error on this on this part of the code

this.errorMessages.get(key)()

Can someone explain why the problem as to why I'm getting this error and a possible solution to the problem?

1 Reply

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Bohdan Stupak4y ago
Accepted answer
Although you perfrom a check for presence of the key, when you do get the type returned is still () =>string | undefined. So once you do get you have to check if the result is not undefined. Or you can perfrom check once like this
return Object.keys(errors).map(
    key => {
        let func = this.errorMessages.get(key)
        if (func != undefined) {
            return func()
        }
        return errors[key] || key;
    });
+1