Angular 6: TypeError - The function you are trying to use is not recognized as a valid function, even though it should be

Question

Angular 6: TypeError - The function you are trying to use is not recognized as a valid function, even though it should be

I'm currently facing a puzzling issue where I'm encountering the

ERROR TypeError: "_this.device.addKeysToObj is not a function"

. Despite having implemented the function, I can't figure out why it's not functioning properly or callable. This error persists when testing the code on both Firefox and Chrome.

The problematic line causing the error is

this.device.addKeysToObj(this.result.results[0]);

Below is the excerpt from my class:

export class Device {
    id: number;
    deviceID: string;
    name: string;
    location: string;
    deviceType: string;
    subType: string;
    valueNamingMap: Object;

    addKeysToObj(deviceValues: object): void {
        for (let key of Object.keys(deviceValues).map((key) => { return key })) {
            if (!this.valueNamingMap.hasOwnProperty(key)) {
                this.valueNamingMap[key] = '';
            }
        }
        console.log(this, deviceValues);
    }
}

And here is how the function is called:

export class BatterieSensorComponent implements OnInit {
    @Input() device: Device;
    public result: Page<Value> = new Page<Value>();

    //[..]

    ngOnInit() {
      this.valueService.list('', this.device).subscribe(
        res => {
          console.log(this.device);  
          this.result = res;
          if (this.result.count > 0) 
          {
            this.device.addKeysToObj(this.result.results[0]);
          }
        }
      )
    }
}

Update:

Upon logging this.device, we get the following output:

{
    deviceID: "000000001" 
    deviceType: "sensor"    
    id: 5    
    location: "-"
    name: "Batteries"    
    subType: "sensor"    
    valueNamingMap:
      Object { v0: "vehicle battery", v1: "Living area battery" }
    prototype: Object { … } 
}

Extra Information:

An excerpt from the device.service code:

list(url?: string, deviceType?: string, subType?: string): Observable<Page<Device>> {
  if(!url) url = `${this.url}/devices/`;
  if(deviceType) url+= '?deviceType=' + deviceType;
  if(subType) url+= '&subType=' + subType;

  return this.httpClient.get<Page<Device>>(url, { headers: this.headers })
    .pipe(
      catchError(this.handleError('LIST devices', new Page<Device>()))
    );
}

The call in the parent component:

ngOnInit() {
  this.deviceService.list('', 'sensor', ).subscribe(
    res => { 
      this.devices = res.results;
    }
  )
}

Template:

<div class="mdl-grid">
  <div class="mdl-cell mdl-cell--6-col mdl-cell--6-col-tablet" *ngFor="let device of devices">
    <app-batterie-sensor [device]="device"></app-batterie-sensor>
  </div>
</div>

javascript angular typescript

Answer 1

Answer №1

Unique answer

This issue is a common pitfall in Typescript. Even though you define the type of device as Device, it may not actually be an instance of Device. While it may have all the properties of a Device, it lacks the expected methods because it's not truly a Device.

To resolve this, make sure to instantiate an actual Device for each entry in your Page. One way to do this is by utilizing the ngOnInit method in the parent component:

If your Page is an array, consider implementing the following:

ngOnInit() {
  this.deviceService.list('', 'sensor').subscribe(
    res => { 
      this.devices = res.results.map(x => Object.assign(new Device(), x));
    }
  )
}

Further insight

Let's explore a typescript example that delves into how this behavior is independent of Angular. We'll use localStorage to simulate data retrieval from an external source, which applies similarly to HTTP calls.

interface SimpleValue {
    a: number;
    b: string;
}

function loadFromStorage<T>(): T {
    const storedValue = localStorage.getItem('MyKey') as string;
    return JSON.parse(storedValue);
}

const valueToSave: SimpleValue = { a: 1, b: 'b' };
localStorage.setItem('MyKey', JSON.stringify(valueToSave));

const loadedValue = loadFromStorage<SimpleValue>();

console.log(loadedValue);

In TypeScript, interfaces serve as compile-time structures and offer no direct representation in JavaScript. This means that if you misuse an interface, the compiler can't catch it at compile time.

Comparatively, loading a class from an external source differs. Classes transpile to their JavaScript equivalents, persisting beyond compilation. The absence of methods when loading a class instance indicates a loss of behavior due to JSON serialization.

Addressing this requires careful design considerations, demonstrated using a common scenario involving dates in Angular with JSON data.

class SimpleClass {
    constructor(public a: number, public b: string) { }

    printA() {
        console.log(this.a);
    }
}

const valueToSave: SimpleClass = new SimpleClass(1, 'b');
localStorage.setItem('MyKey', JSON.stringify(valueToSave));

const loadedValue = loadFromStorage<SimpleClass>();

// TypeError occurs due to lost methods
loadedValue.printA();

An effective pattern for managing frontend models sourced from flat backend contracts involves explicit mapping strategies within constructors or leveraging tools like Object.assign for flexibility and robustness.

Answer 2

Unique answer

This issue is a common pitfall in Typescript. Even though you define the type of device as Device, it may not actually be an instance of Device. While it may have all the properties of a Device, it lacks the expected methods because it's not truly a Device.

To resolve this, make sure to instantiate an actual Device for each entry in your Page. One way to do this is by utilizing the ngOnInit method in the parent component:

If your Page is an array, consider implementing the following:

ngOnInit() {
  this.deviceService.list('', 'sensor').subscribe(
    res => { 
      this.devices = res.results.map(x => Object.assign(new Device(), x));
    }
  )
}

Further insight

Let's explore a typescript example that delves into how this behavior is independent of Angular. We'll use localStorage to simulate data retrieval from an external source, which applies similarly to HTTP calls.

interface SimpleValue {
    a: number;
    b: string;
}

function loadFromStorage<T>(): T {
    const storedValue = localStorage.getItem('MyKey') as string;
    return JSON.parse(storedValue);
}

const valueToSave: SimpleValue = { a: 1, b: 'b' };
localStorage.setItem('MyKey', JSON.stringify(valueToSave));

const loadedValue = loadFromStorage<SimpleValue>();

console.log(loadedValue);

In TypeScript, interfaces serve as compile-time structures and offer no direct representation in JavaScript. This means that if you misuse an interface, the compiler can't catch it at compile time.

Comparatively, loading a class from an external source differs. Classes transpile to their JavaScript equivalents, persisting beyond compilation. The absence of methods when loading a class instance indicates a loss of behavior due to JSON serialization.

Addressing this requires careful design considerations, demonstrated using a common scenario involving dates in Angular with JSON data.

class SimpleClass {
    constructor(public a: number, public b: string) { }

    printA() {
        console.log(this.a);
    }
}

const valueToSave: SimpleClass = new SimpleClass(1, 'b');
localStorage.setItem('MyKey', JSON.stringify(valueToSave));

const loadedValue = loadFromStorage<SimpleClass>();

// TypeError occurs due to lost methods
loadedValue.printA();

An effective pattern for managing frontend models sourced from flat backend contracts involves explicit mapping strategies within constructors or leveraging tools like Object.assign for flexibility and robustness.

Answer 3

Answer №2

Arriving here may present you with a different issue compared to the solution provided: If you are utilizing Angular's services and happen to overlook adding @Injectable, under Angular Ivy, you will encounter a runtime error similar to this:

ERROR TypeError: ConfigurationServiceImpl.\u0275fac is not a function

The proper resolution is to include @Injectable when defining implementations, for instance:

// be sure to include @Injectable(), or else an error will arise!
@Injectable()
export class ConfigurationServiceImpl implements ConfigurationService {
...
}

@Injectable({
  providedIn: "root",
  useClass: ConfigurationServiceImpl,
})
export abstract class ConfigurationService {
...
}

For more information, refer to Angular 7 TypeError: service.x is not a function.

Answer 4

Arriving here may present you with a different issue compared to the solution provided: If you are utilizing Angular's services and happen to overlook adding @Injectable, under Angular Ivy, you will encounter a runtime error similar to this:

ERROR TypeError: ConfigurationServiceImpl.\u0275fac is not a function

The proper resolution is to include @Injectable when defining implementations, for instance:

// be sure to include @Injectable(), or else an error will arise!
@Injectable()
export class ConfigurationServiceImpl implements ConfigurationService {
...
}

@Injectable({
  providedIn: "root",
  useClass: ConfigurationServiceImpl,
})
export abstract class ConfigurationService {
...
}

For more information, refer to Angular 7 TypeError: service.x is not a function.

Answer 5

Answer №3

After experimenting with different approaches, I found two solutions that worked well for me

One method involved wrapping the code in a setTimeout

ngOnInit() {
  setTimeOut({ // START OF SETTIMEOUT
    this.deviceService.list('', 'sensor', ).subscribe(
      res => { 
        this.devices = res.results.map(x => Object.assign(new Device(), x));
      }
    )
  }); // END OF SETTIMEOUT
}

Alternatively

The other solution required adding a condition

ngOnInit() {
  if(typeof this.deviceService.list === 'function'){ // START OF CONDITION
    this.deviceService.list('', 'sensor', ).subscribe(
      res => { 
        this.devices = res.results.map(x => Object.assign(new Device(), x));
      }
    )
  } // END OF CONDITION
}

Answer 6

After experimenting with different approaches, I found two solutions that worked well for me

One method involved wrapping the code in a setTimeout

ngOnInit() {
  setTimeOut({ // START OF SETTIMEOUT
    this.deviceService.list('', 'sensor', ).subscribe(
      res => { 
        this.devices = res.results.map(x => Object.assign(new Device(), x));
      }
    )
  }); // END OF SETTIMEOUT
}

Alternatively

The other solution required adding a condition

ngOnInit() {
  if(typeof this.deviceService.list === 'function'){ // START OF CONDITION
    this.deviceService.list('', 'sensor', ).subscribe(
      res => { 
        this.devices = res.results.map(x => Object.assign(new Device(), x));
      }
    )
  } // END OF CONDITION
}

Answer 7

Answer №4

As mentioned by @UncleDave earlier, the process of mapping values with corresponding names to a Typescript object does not create the expected class object. This can be quite confusing.

Object.assign() can resolve the current issue, but it may not work effectively for nested objects. In such cases, you would need to apply Object.assign() recursively for each nested object, which could become cumbersome if done in multiple instances within your codebase.

An alternative solution is recommended: using class-transformer. With this approach, you can annotate nested fields to instruct the compiler on how to generate the nested objects as required. By using the plainToClass() method, you can map the top-level object and ensure that all underlying fields possess the correct types/objects.

Example

Consider two classes:

class Parent {
    name: string;
    child: Child;

    public getText(): string {
        return 'parent text';
    }
}

class Child{
    name: string;

    public getText(): string {
        return 'child text';
    }
}

In the initial case, direct assignment doesn't function correctly:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = parentJson; // Compiler allows this due to the type being any.  
// Directly assigning the json structure to 'parent' would result in an error due to missing methods like getText().

console.log(parent.getText()); // Error occurs as expected since parent.getText() is not a valid function

In the second situation utilizing Object.assign():

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = Object.assign(parentJson); 

console.log(parent.getText()); // Works fine
console.log(parent.child.getText()); // Results in an error stating that parent.child.getText() is invalid

To make it function properly, the following steps are necessary:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = Object.assign(parentJson);
parent.child = Object.assign(parentJson.child);

console.log(parent.getText()); // Works correctly
console.log(parent.child.getText()); // Functions as expected now

In the third scenario employing class-transformer:

Begin by modifying the parent class to define the child mapping:

class Parent {
    name: string;
    @Type(() => Child)
    child: Child;

    public getText(): string {
        return 'parent text';
    }
}

Subsequently, map to the parent object accordingly:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = plainToClass(Parent, parentJson);

console.log(parent.getText()); // Functions correctly
console.log(parent.child.getText()); // Executes as intended

Answer 8

As mentioned by @UncleDave earlier, the process of mapping values with corresponding names to a Typescript object does not create the expected class object. This can be quite confusing.

Object.assign() can resolve the current issue, but it may not work effectively for nested objects. In such cases, you would need to apply Object.assign() recursively for each nested object, which could become cumbersome if done in multiple instances within your codebase.

An alternative solution is recommended: using class-transformer. With this approach, you can annotate nested fields to instruct the compiler on how to generate the nested objects as required. By using the plainToClass() method, you can map the top-level object and ensure that all underlying fields possess the correct types/objects.

Example

Consider two classes:

class Parent {
    name: string;
    child: Child;

    public getText(): string {
        return 'parent text';
    }
}

class Child{
    name: string;

    public getText(): string {
        return 'child text';
    }
}

In the initial case, direct assignment doesn't function correctly:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = parentJson; // Compiler allows this due to the type being any.  
// Directly assigning the json structure to 'parent' would result in an error due to missing methods like getText().

console.log(parent.getText()); // Error occurs as expected since parent.getText() is not a valid function

In the second situation utilizing Object.assign():

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = Object.assign(parentJson); 

console.log(parent.getText()); // Works fine
console.log(parent.child.getText()); // Results in an error stating that parent.child.getText() is invalid

To make it function properly, the following steps are necessary:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = Object.assign(parentJson);
parent.child = Object.assign(parentJson.child);

console.log(parent.getText()); // Works correctly
console.log(parent.child.getText()); // Functions as expected now

In the third scenario employing class-transformer:

Begin by modifying the parent class to define the child mapping:

class Parent {
    name: string;
    @Type(() => Child)
    child: Child;

    public getText(): string {
        return 'parent text';
    }
}

Subsequently, map to the parent object accordingly:

let parentJson: any = {name: 'parent name', child: {name: 'child name'}};
let parent: Parent = plainToClass(Parent, parentJson);

console.log(parent.getText()); // Functions correctly
console.log(parent.child.getText()); // Executes as intended

Answer 9

Answer №5

After watching a YT video, I found the answer to my problem in this post. It mentioned checking if the method of that specific class exists.

Answer 10

After watching a YT video, I found the answer to my problem in this post. It mentioned checking if the method of that specific class exists.

Angular 6: TypeError - The function you are trying to use is not recognized as a valid function, even though it should be

Answer №1

Unique answer

Further insight

Answer №2

Answer №3

Answer №4

Example

Answer №5

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