And the vendor prefixes attack again. This time, the ordinal indexing of the CSSStyleDeclaration is being used to see what the "first" vendor prefix is within the list of parser names supported by the browser. Since -ms- comes before -webkit- it will prioritize that over anything else. Also, the implicit assumption that if you support one vendor…

evil_vendor_prefix2.js

// Utilize duck typed slice, to enumerate 0..length indices.
// Indices on CSSStyleDeclaration return the "parser" names for properties.
// Based on the parser names, determine the vendor prefix to use.
var vendor_prefix = Array.prototype.slice.call(window.getComputedStyle(document.body)).join('').match(/-(ms|webkit|moz)-/)[0];
console.log(vendor_prefix);