var to5 = require('6to5');
var result = to5.transform('let foo = {bar: "baz"};\n var {bar} = foo;', {filename:'foo.js',sourceMap: true});
var sourceMap = result.split('\n').splice(-2, 1)[0].slice(50);
console.log((new Buffer(sourceMap, 'base64')).toString());
// {"version":3,"sources":[],"names":[],"mappings":"","sourcesContent":[]}