How to declare Return Types for Functions in TypeScript

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You are correct – here is a fully working example – you’ll see that var result is implicitly a string because the return type is specified on the greet() function. Change the type to number and you’ll get warnings.

class Greeter {
    greeting: string;
    constructor (message: string) {
        this.greeting = message;
    }
    greet() : string {
        return "Hello, " + this.greeting;
    }
} 

var greeter = new Greeter("Hi");
var result = greeter.greet();

Here is the number example – you’ll see red squiggles in the playground editor if you try this:

greet() : number {
    return "Hello, " + this.greeting;
}

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