Typescript - How do I add an extension method

问题

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?

回答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) };

Playground

回答2:

You could extend the String interface, like this:

interface String {
    toNumber(): number;
}

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

const s = '123.45';
s.toNumber();

来源：https://stackoverflow.com/questions/59089145/typescript-how-do-i-add-an-extension-method