Angular error: Trying to access the toLowerCase property of an undefined value

I am facing an issue wherein, when I use the http.post method, I encounter an error stating "TypeError: Cannot read property 'toLowerCase' of undefined". I have attempted to downgrade Angular to version 8.0.0 in order to resolve this problem, but to no avail.

Here is my login service code:

login(model: any)
 {
    return this.http.post(this.baseUrl, model)
    .pipe(map((response: any) => {
      const user = response;
      if(user){
        localStorage.setItem('token', user);
      }
    }));
 }

This is how I call the login method in my component:

login(){
    this.authService.login(this.model)
        .subscribe(next =>{
          console.log('You have been logged in');
        },err => {
          console.log(err);
        });
  }

Answer №1

It appears that the issue lies in how you have declared your baseUrl. It seems like you are defining the type of baseUrl rather than assigning a value to it. Remember, using : assigns a type and = assigns a value. You might have something similar to this in your code:

  private baseUrl: 'http://localhost:3000/';

If we try to console.log the type of baseUrl, it will display as undefined:

 console.log(typeof this.usersUrl);
 // returns undefined

Similarly, when you try to log the actual value of baseUrl, it will again show up as undefined:

 console.log(this.usersUrl);
 // returns undefined

You can see an example of this issuehere.

To resolve this, simply update the declaration of baseUrl and assign a string value to it:

  private baseUrl: string = 'http://localhost:3000/';

Explaining why the error points to the toLowercase method

The reason you are receiving the error

TypeError: Cannot read property 'toLowerCase' of undefined"
is because Angular attempts to convert the string baseUrl into lowercase using the native toLowercase method. Since baseUrl is not correctly defined in your code as a string, the error occurs due to the lack of definition.

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