FlowType.JS

FlowType is a handy jquery plugin that allows you to set maximum and minimum widths on content elements to ensure a lovely typographical flow.

If the first thing you do is think about the performance implications of this tool then aside from commending you for doing so I can also tell you to relax and check out their demo coving this exact concern.

The plugin maintains the 45-75 character best practice limit on a line for most legible typography. Unfortunately this can look rather disastrous when approaching small viewports as 45  characters on a 300px wide screen is a little too small.

Fortunately you can set minimum and maximum thresholds for media queries, font size and line height to counteract any excessively small or large viewports. The best thing of all is it is a progressive enhancement you can add on if or when required.