$ echo '/*@const*/ var b = 1; b = 2; console.log(1+b);' | node
3

$ echo '/*@const*/ var b = 1; b = 2; console.log(1+b);' | uglifyjs -c
var b=1;b=2,console.log(2);

$ echo '/*@const*/ var b = 1; b = 2; console.log(1+b);' | uglifyjs -c | node
2