What is metadata rewriting?

Metadata rewriting is the process in which the compiler converts the expression initializing the fields such as useClass, useValue, useFactory, and data into an exported variable, which replaces the expression. Remember that the compiler does this rewriting during the emit of the .js file but not in definition files( .d.ts file).

Practical Code Example

// Metadata Rewriting:
// AOT compiler rewrites expressions in decorators into static representations
// to support library code distribution without shipping raw TypeScript source files.