Where does the lib come from in typecsript?


I have a typescript@2 project. I wanted to use some ecma2017 features. I found out that one can apply a lib in the compilerOptions in the tsconfig.json:

"target": "es6",
"lib": [

Yet why is this working? Where do these lib come from, what libs can one include?

The closest to a documentation I could find was this this what’s new entry:

Downlevel Async Functions

This feature was supported before TypeScript 2.1, but only when targeting ES6/ES2015. TypeScript 2.1 brings the capability to ES3 and
ES5 run-times, meaning you’ll be free to take advantage of it no
matter what environment you’re using.

Note: first, we need to make sure our run-time has an ECMAScript-compliant Promise available globally. That might involve
grabbing a polyfill for Promise, or relying on one that you might have
in the run-time that you’re targeting. We also need to make sure that
TypeScript knows Promise exists by setting your lib flag to something
like “dom”, “es2015” or “dom”, “es2015.promise”, “es5”

yet I didn’t find it particular helpful.


All values of the compiler options lib is referenced in the Lib documentation:

List of library files to be included in the 

Possible values are: 
► ES5 
► ES6 
► ES2015 
► ES7 
► ES2016 
► ES2017 
► ESNext 
► DOM 
► DOM.Iterable 
► WebWorker 
► ScriptHost 
► ES2015.Core 
► ES2015.Collection 
► ES2015.Generator 
► ES2015.Iterable 
► ES2015.Promise 
► ES2015.Proxy 
► ES2015.Reflect 
► ES2015.Symbol 
► ES2015.Symbol.WellKnown 
► ES2016.Array.Include 
► ES2017.object 
► ES2017.SharedMemory 
► esnext.asynciterable 

Note: If --lib is not specified a default library is injected. The default library injected is: 
► For --target ES5: DOM,ES5,ScriptHost
► For --target ES6: DOM,ES6,DOM.Iterable,ScriptHost

Answered By – HolgerJeromin

Answer Checked By – Marilyn (AngularFixing Volunteer)

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