What is ambient in TypeScript

0 votes

I don't understand what means the word ambient in the following sentence:

A function implementation cannot be declared in an ambient context.

I'm not sure to understand the general meaning of the word, (English isn't my maternal language) and if there is a specific meaning here I don't get it as well.

I've tried to understand in my maternal language but couldn't get it in this context. It's something like current context I'd say but it doesn't work out.

The message appeared because I was trying to declare a class, which cannot be declared, only module can. I've fixed it but still don't understand the meaning of the error message here.

Jun 16, 2022 in TypeSript by Logan
• 2,140 points
1,076 views

1 answer to this question.

0 votes

Ambient simply means "without implementation".

Ambient declarations only exist in the type system and are erased at run-time:

// ambient module declaration
declare module "mymod" { /*... */ }

// ambient namespace declaration
declare namespace MyNamespace { /*... */ }

// ambient variable declaration
declare const myVar: string;

For example declare const myVar: string is like a promise to the compiler: "Assume that there will be a const myVar with type string defined at run-time" (other cases analogue).

You also can think of ambient as the declare keyword in TS. All type declarations like interfaces or type aliases are implicitly ambient by definition, as it is clear for the compiler, that these have no run-time impact.

declare type MyType = {a: string} // is valid
type MyType = {a: string} // shorter, so just leave "declare" out

"A function implementation cannot be declared in an ambient context."

As said, ambient declarations cannot contain run-time code, like:

declare module "mymod" {
    function foo() { // error: An implementation cannot be declared in ambient contexts.
        console.log("bar")
    }
}

Given "mymod" is a npm package, the implementation code would rather be in the main .js file under "node_modules/mymod", and above types reside in a separate .d.ts file.

answered Jun 22, 2022 by Nina
• 3,060 points

Related Questions In TypeSript

0 votes
1 answer

What is record in TypeScript

A Record<K, T> is an object type whose property ...READ MORE

answered Jun 7, 2022 in TypeSript by Nina
• 3,060 points
6,174 views
0 votes
0 answers

What is a type in Typescript for the Component class in Angular 2+?

I have a small problem, but big ...READ MORE

Jul 5, 2022 in TypeSript by Logan
• 2,140 points
508 views
0 votes
0 answers

What is TypeScript and why would I use it in place of JavaScript?

Can you please describe what the TypeScript ...READ MORE

Jul 18, 2022 in TypeSript by Logan
• 2,140 points
189 views
0 votes
1 answer

What is the question mark for in a Typescript parameter name?

It is to mark the parameter as optional. TypeScript ...READ MORE

answered Aug 3, 2022 in TypeSript by Abhinaya
• 1,160 points
966 views
0 votes
1 answer

How to set meta tags using Angular universal SSR and ngx-seo plug-in?

first Install the plug-in with npm i ngx-seo ...READ MORE

answered Feb 11, 2022 in Others by narikkadan
• 63,420 points
1,898 views
0 votes
1 answer

Can't bind to 'ngModel' since it isn't a known property of 'input'

Just add this in the app.module.ts file: import { FormsModule ...READ MORE

answered Apr 30, 2022 in Other DevOps Questions by narikkadan
• 63,420 points
3,882 views
0 votes
1 answer

VS Code enforces semicolons, but why doesn't Angular and TypeScript not use it consistently?

JavaScript has a syntactic feature known as semicolon ...READ MORE

answered May 31, 2022 in TypeSript by Nina
• 3,060 points
4,165 views
0 votes
1 answer

Square brackets around vs after expression in Typescript

x is an Array, while y is a Tuple. The ...READ MORE

answered Jun 7, 2022 in TypeSript by Nina
• 3,060 points
3,138 views
0 votes
1 answer

What is TypeScript and why would I use it in place of JavaScript?

TypeScript is a superset of JavaScript which primarily ...READ MORE

answered May 31, 2022 in TypeSript by Nina
• 3,060 points
302 views
0 votes
1 answer

What is "not assignable to parameter of type never" error in TypeScript?

All you have to do is define ...READ MORE

answered May 31, 2022 in TypeSript by Nina
• 3,060 points
46,999 views
webinar REGISTER FOR FREE WEBINAR X
REGISTER NOW
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP