Typescript error “Cannot find name”

Question

I am trying to use the big.js library, whose definition is here .

Now, this line works:

const CONSTANT_1 = new Big(0);

Whilst this line:

const CONSTANT_2 : Big = new Big(0);

causes the error:

error TS2304: Cannot find name 'Big'.

What's the problem?

Answer 1

Look at what the first one is implicitly typed as:

Problem

The reason that this doesn't work...

const CONSTANT_2: Big = new Big(0);

...is because Big is defined as a variable in the definition file—not a type:

declare var Big: BigJsLibrary.BigJS;

Solution

If you wish to use explicit typing then you need to reference the created type of the constructor...

const CONSTANT_2: BigJsLibrary.BigJS = new Big(0);

...as is shown in the definition file here:

interface BigJS_Constructors {
    new (value: number): BigJS;
    // etc...
}