Uncaught SyntaxError: Unexpected token ILLEGAL

the index.js has a lot of special characters. I'm using babelify to transform the project. Any idea?
var ε = 1e-6,
ε2 = ε \* ε,
Ï€ = Math.PI,
τ = 2 \* π,
τε = τ - ε,
halfπ = π / 2,
d3_radians = π / 180,
d3_degrees = 180 / π;