d3.tip: Tooltips for d3.js Version 4, without ES6

See a live example.

Origins

While it hasn't been updated since 2015, the popular d3-tip code from Justin Palmer (Caged on github; http://github.com/Caged/d3-tip) has been widely used with d3js version 3. I was one of those users.

With the release of d3js version 4, the old d3-tip code no longer worked. Thanks to a fork from Constantin Gavrilete (cgav on github; https://github.com/cgav), the code was updated to work with d3js version 4. However, this new version from cgav used the JavaScript ES6 import statement, which is not widely supported in today's browsers.

I needed a version that was both D3js v4 and standard-browser compatible.

Using d3-tip with D3js v4, without ES6

The version of d3-tip in this repository is D3js v4 compatible. At the same time, it does not require ES6 support from your browser. This is accomplished with two basic changes.

1. d3.functor is defined. This was defined in version 3 of D3, but disappeared in version 4. It gets redefined in this version of d3-tip.

2. d3.tip is defined. This mimics the prior behavior of d3-tip, allowing you to use tooltips as documented in the original repository (https://github.com/Caged/d3-tip).