Overwrite function in TypeScript

Question

alert = (function (origAlert) {
    return function (...messages: any[]) {
        origAlert(messages.join(" "))
    }
})(alert)

// Example
alert(1, 2)

I want to overwrite / redefine the function alert(message?: any) which has already been declared in lib.d.ts before: declare function alert(message?: any): void;

But alert = function... throws "Invalid left-hand side of assignment expression."

The point is that, function alert(...messages: any[]) { /* ... */ } ~~would work~~* does not even work as well, but I need to use the original alert. And I'd dislike to define an extra const origAlert = alert before the function.

How can I do this?

Note that the compiled JavaScript in the Playground works as intended.

*on TypeScript Playground it works, but in Visual Studio it throws "Overload signatures must all be ambient or non-ambient"

I don't know what the intended use of your code is. However, if you need it for debugging, then I would just use console.log(). Otherwise, it's a bad idea to redefine native functions, often it backfires. — MartyIX
– MartyIX, Commented Dec 12, 2015 at 11:57

RomkaChev · Accepted Answer · 2015-12-12 10:10:53Z

0

declare function alert(...messages: any[]): void;

window.alert = ((orig) => {
    return (...messages: any[]) => orig(messages.join(" "));
})(alert);

alert(1, 2)

answered Dec 12, 2015 at 10:10

RomkaChev

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5 Comments

CoderPi Over a year ago

That hack works for this, thanks^^ I'll still hope someone can find a general solution

RomkaChev Over a year ago

these error messages is not clear enough - look at github.com/Microsoft/TypeScript/issues/2474. I doubt that someone will make a general solution. P.S. I hope that I am wrong)

CoderPi Over a year ago

Also Playground is compiling it just as it should.. that's really strange

Nypan Over a year ago

The compiler will output results even if there are transpilation errors, the flag noEmitOnError changes this behaviour.

RomkaChev Over a year ago

It's compiled because of this hack do not owerwrites original lib.d.ts file declare function alert(message?: any): void; // this stuff following code tries to overwrite declare function like it's a variable alert = function(/**/){/**/} So, hacks is our everything. PS Sorry for engrish.

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