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Generic Return Type, Optional Parameter and Default Value

Generic Return Type, Optional Parameter and Default Value

In this lesson, you will cover the concept of the generic return type, optional parameter, and default value.

We'll cover the following...

Function’s generic return type

TypeScript, since version 2.4, can infer the type of a function’s return value. Before version 2.4, s.length would give an error. The s was not from a U[] type but an empty object literal {}.

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function arrayMap<T, U>(f: (x: T) => U): (a: T[]) => U[] {     
  return a => a.map(f); 
} 
const lengths: (a: string[]) => number[] = arrayMap(s => s.length);

Function’s optional parameters

TypeScript lets you have optional parameters with different syntax. The ...