is-undefined

Determine if a value is undefined.

Usage

    npm install @primitive/is-undefined --save   # Install package via NPM
    yarn add @primitive/is-undefined             # Install package via Yarn

    import { expect } from "chai";
    import isUndefined from "@primitive/is-undefined";

    expect(isUndefined(({ x: 42 }).y)).to.be.true;
    expect(isUndefined(undefined)).to.be.true;
    expect(isUndefined(void 0)).to.be.true;

    expect(isUndefined(null)).to.be.false;
    expect(isUndefined(42)).to.be.false;

This package contains TypeScript type declarations. Furthermore, the package uses TypeScript type guards to allow type inference to influence intellisense.

    if (isUndefined(x)) {
        // IntelliSense now knows `x` is `undefined`.
        let y: undefined = x;
    }

Content Delivery Network (CDN)

This package can be imported via unpkg as demonstrated below.

    <script src="https://unpkg.com/@primitive/is-undefined/dist/index.min.js">
    <script type="application/javascript">
        var x = undefined;
        if (isUndefined(x)) {
            // `x` is `undefined`!
        }
    </script>

Build & Test

This package uses Gulp for building, and Chai and Mocha for testing.

    npm install     # Installs dependencies.
    npm run build   # Build the project.
    npm test        # Run tests.

License

Refer to the LICENSE file for license information.