Typescript - How do I add an extension method

Question

I read that you can create extension methods in Typescript and I looked up some code

And put that code in my extension methods.ts but I get an error saying that toNumber doesn't exist. How can I fix this?

Answer 1

You can extend String interface by augmenting global scope:

export { };

declare global {
    interface String {
        toNumber(): number;
    }
}

String.prototype.toNumber = function (this: string) { return parseFloat(this) };

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