Suppose i want to extend String.prototype, so i have this in ext/string.ts for example:

interface String {
    contains(sub: string): boolean;
}

String.prototype.contains = function (sub:string):boolean {
    if (sub === "") {
        return false;
    }
    return (this.indexOf(sub) !== -1);
};

When i do import * as string from 'ext/string.ts' it fails with this error:

error TS2306: File 'ext/string.ts' is not a module

and this is supposed behavior , i didn't write export. But how do i tell to Typescript that i want to extend String.prototype then?

Suppose i want to extend String.prototype, so i have this in ext/string.ts for example:

interface String {
    contains(sub: string): boolean;
}

String.prototype.contains = function (sub:string):boolean {
    if (sub === "") {
        return false;
    }
    return (this.indexOf(sub) !== -1);
};

When i do import * as string from 'ext/string.ts' it fails with this error:

error TS2306: File 'ext/string.ts' is not a module

and this is supposed behavior , i didn't write export. But how do i tell to Typescript that i want to extend String.prototype then?

• javascript
• typescript
• typescript1.8

Share Improve this question Follow edited May 3, 2016 at 12:54 Ahmed farag mostafa 2,97422 gold badges1616 silver badges3333 bronze badges asked May 3, 2016 at 12:33 layaboutlayabout 19911 silver badge1515 bronze badges 1

• Honestly, you should really consider not extending the built-in types like this. When some future ES version es out with its own native implementation of contains your code will override that and possibly be slower than the native code. See stackoverflow./q/14034180/215552. – Heretic Monkey Commented May 3, 2016 at 14:05

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1 Answer 1

Sorted by: Reset to default 12

You just need to run the file without importing anything. You can do that with this code:

import "./ext/string";

---

However, if your string.ts file contains any import statements then you will need to take out the interface and put it in a definition file (.d.ts). You need to do this with external modules so that the piler knows it needs to be merged with the String interface in the global scope. For example:

// customTypings/string.d.ts
interface String {
    contains(sub: string): boolean;
}

// ext/string.ts
String.prototype.contains = function(sub:string): boolean {
    if (sub === "") {
        return false;
    }
    return (this.indexOf(sub) !== -1);
};

// main.ts
import "./ext/string";

"some string".contains("t"); // true