Is there a way to inform TypeScript of the existence of a value?

Question

Is there a way to inform TypeScript of the existence of a value?

I am facing an issue with the code below:

   options: { url?: string } = {};
   if (!Checker.present(this.options.url)) {
      throw new Error('Options must have a url');
   }
   new CustomUrl(this.options)

This error is occurring because CustomUrl requires a url, but my interface has made it optional.

The function I use for checking looks like this:

  static present(value: any) {
    return value !== undefined && value !== null;
  }

However, I am unsure how to communicate to TypeScript that I have checked and confirmed the presence of a value without using the ! operator in my code. Any suggestions?

typescript

Answer 1

Answer №1

To ensure that the object has a "url" property, you can use the as keyword:

new CustomUrl(this.options as { url: string });

If you want to combine an optional interface with a mandatory "url" property in a more general scenario, you can use & { url: string }:

new CustomUrl(this.options as Options & { url: string });

In this case, Options represents the type of the initial options.

Answer 2

To ensure that the object has a "url" property, you can use the as keyword:

new CustomUrl(this.options as { url: string });

If you want to combine an optional interface with a mandatory "url" property in a more general scenario, you can use & { url: string }:

new CustomUrl(this.options as Options & { url: string });

In this case, Options represents the type of the initial options.

Answer 3

Answer №2

To effectively utilize the CustomUrl function, you must confirm the presence of the URL within the function itself, rather than externally.


interface IOpt{
    { url?: string } 
}

function CustomUrl(opt:Required<IOpt>){
}

Alternatively, You should modify the parameter of the CustomUrl function to be Required.


interface IOpt{
    { url?: string } 
}

function CustomUrl(opt:Required<IOpt>){
}

Answer 4

To effectively utilize the CustomUrl function, you must confirm the presence of the URL within the function itself, rather than externally.


interface IOpt{
    { url?: string } 
}

function CustomUrl(opt:Required<IOpt>){
}

Alternatively, You should modify the parameter of the CustomUrl function to be Required.


interface IOpt{
    { url?: string } 
}

function CustomUrl(opt:Required<IOpt>){
}

Is there a way to inform TypeScript of the existence of a value?

Answer №1

Answer №2

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