bigint-lib v1.1.0

bigint-lib

Use BigInt in library code, whether native or polyfilled.

Installation

npm install --save bigint-lib

Usage

If polyfilling, polyfill BigInt first.

Then,

import {bigIntLib} from "bigint-lib";

/**
 * `true` if natively supported; `false` otherwise
 */
bigIntLib.isNativelySupported();

/**
 * `true` if considered a `BigInt`
 */
bigIntLib.isBigInt(x);

/**
 * Creates a `BigInt` instance
 */
bigIntLib.BigInt(0);

See API for more details

Since this library is meant for library authors, reading the source code to understand how it works internally is recommended.

Motivation

Not all browsers support BigInt natively.

https://caniuse.com/#feat=mdn-javascript_builtins_bigint

Application code can use polyfills for BigInt easily.

https://github.com/GoogleChromeLabs/jsbi

However, libraries cannot assume that BigInt is natively supported, or polyfilled.

A library has to check.

If it is natively supported, we can use BigInt and all built-in operations directly.

If it is polyfilled, we cannot assume the shape of the exposed API for built-in operations.

Is addition done with x.add(y)? Or Polyfill.add(x, y)? Or x.plus(y)? Is it even implemented at all?

What about every other operation?

This library provides a unified API for all built-in BigInt operations, regardless of whether BigInt is natively supported, or polyfilled.

How it works

This library's only dependency is jsbi.

We have three cases to handle,

• BigInt is natively supported

  We use the built-in operations directly.

  This is the most efficient.

  See src/native.ts for more details.

• BigInt is polyfilled using jsbi

  We use jsbi for built-in operations.

  This is still pretty efficient.

  See src/jsbi-polyfill.ts for more details.

• BigInt is polyfilled using some other library

  We convert the other library's BigInt to JSBI, use jsbi for built-in operations, and convert the result back to the other libary's BigInt.

  This is the least efficient, but saves us from having to worry about the exposed API of the other library.

  See src/non-jsbi-polyfill.ts for more details.

Expected Polyfill

This library assumes polyfills conform to some minimal API.

Polyfill with JSBI

To polyfill using jsbi,

import JSBI from "jsbi";
global.BigInt = JSBI.BigInt;

At the moment, using jsbi+TypeScript with esModuleInterop:false may cause the import to fail during run-time.

You may set esModuleInterop:true to fix the problem. However, setting esModuleInterop:true may cause other imports to fail.

You may choose to keep esModuleInterop:false and change the import to,

import {JSBI} from "bigint-lib/dist/jsbi";
global.BigInt = JSBI.BigInt;

Polyfill with Other Library

If polyfilling with some other library, the library must, minimally, have the following API,

class MyPolyfill {
    constructor (mixed : any) {
        //snip https://tc39.es/ecma262/#sec-bigint-constructor
    }

    toString () {
        return //snip base-10 string
    }
}
global.BigInt = (mixed : any) => new MyPolyfill(mixed);

The polyfill must also satisfy the following properties,

BigInt(0) instanceof MyPolyfill
> true
Object.getPrototypeOf(BigInt(0)).constructor === MyPolyfill
> true

API

The following are exported by this library,

• BigIntLib is the unified API, for native and polyfilled BigInt operations.
• getBigIntLib() returns an instanceof BigIntLib, depending on whether BigInt is native or polyfilled. See How it works for more details.
• JSBI is a re-export of jsbi
• bigIntLib is of type BigIntLib and is initialized with getBigIntLib() when bigint-lib is first imported.
• biLib is a synonym for bigIntLib; in case bigIntLib is too verbose
• nativeBigIntLib is a BigIntLib instance that assumes BigInt is natively supported.
• jsbiPolyfillBigIntLib is a BigIntLib instance that assumes BigInt is polyfilled with jsbi.
• getNonJsbiPolyfillBigIntLib() returns a BigIntLib instance that assumes BigInt is polyfilled with some other library.
• getNativeOrJsbiPolyfillBigIntLib() returns a nativeBigIntLib or jsbiPolyfillBigIntLib, depending on whether BigInt is natively supported or polyfilled.
• nativeOrJsbiLib is a BigIntLib instance and is initialized with getNativeOrJsbiPolyfillBigIntLib() when bigint-lib is first imported.

BigIntLib

The interface is mostly the same as jsbi's

nativeOrJsbiLib

If global.BigInt is natively supported, returns nativeBigIntLib. Otherwise, returns jsbiPolyfillBigIntLib.

This is useful for libraries that need to perform many complex BigInt operations before returning a result.

import {bigIntLib, nativeOrJsbiLib} from "bigint-lib";

const my1 = nativeOrJsbiLib.BigInt(1);

//Takes native or JSBI polyfilled bigints
//Will return a native or JSBI polyfilled bigint
function myComplexFunctionImpl (m : bigint, n : bigint) : bigint {
    if (nativeOrJsbiLib.equal(m, 0)) {
        return nativeOrJsbiLib.add(n, my1);
    }
    if (nativeOrJsbiLib.equal(n, 0)) {
        return myComplexFunctionImpl(
            nativeOrJsbiLib.subtract(m, my1),
            my1
        );
    }
    return myComplexFunctionImpl(
        nativeOrJsbiLib.subtract(m, my1),
        myComplexFunctionImpl(m, nativeOrJsbiLib.subtract(n, 1))
    );
}

//Takes native, JSBI polyfilled, or other polyfilled bigints
//Must return a `bigint` that may be native, polyfilled with JSBI, or polyfilled with other libraries
function myComplexFunction (m : bigint, n : bigint) : bigint {
    //Will be a native or JSBI polyfilled `bigint`
    const myM = nativeOrJsbiLib.BigInt(m.toString());
    const myN = nativeOrJsbiLib.BigInt(n.toString());
    const myResult = myComplexFunctionImpl(myM, myN);

    //Convert the result to a `bigint` type the same as its input
    return bigIntLib.BigInt(myResult.toString());
}

Using nativeOrJsbiLib saves the time needed to convert between JSBI and other polyfill libraries, if other polyfill libraries are used.

Polyfilling with node

1. Have your polyfill code in a .js file.
2. node -r my-polyfill.js my-entry-point.js

Polyfilling with ts-node

1. Have your polyfill code in a .ts file.
2. ts-node -r my-polyfill.ts my-entry-point.ts

Development

1. git clone https://github.com/AnyhowStep/bigint-lib.git
2. npm install
3. npm run sanity-check to build and run tests.
4. npm run to see a list of commands.