Typescript extension method compiling but not working at run time

问题

I have extended the String prototype in Typescript with a simple method:

StringExtensions.ts

String.prototype.toCleanedTitleCase = function ():string {
    let titleCase = this.replace(/\w\S*/g, function (txt) {
        return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase()
    })
    return titleCase.replace(new RegExp(" ", 'g'), "").replace(new RegExp("-", 'g'), "")
}

Then added an interface in a definition file:

StringExtensions.d.ts

interface String {
    toCleanedTitleCase():String;
}

Then calling it:

index.ts

console.log(("Some string that needs a-sorting").toCleanedTitleCase();

All compiles fine, but when I run my app (node js), I get "xxx.toCleanedTitleCase" is not a function.

Any ideas what I'm missing?

来源：https://stackoverflow.com/questions/37438151/typescript-extension-method-compiling-but-not-working-at-run-time