Json.parse error in jsb with some string

[kawais]

var x="%7B%22str%22%3A%22%7B%5C%22iv%5C%22%3A%5C%22wt5AsR8BtNteecathMxjnQ%3D%3D%5C%22%2C%5C%22v%5C%22%3A1%2C%5C%22iter%5C%22%3A1000%2C%5C%22ks%5C%22%3A256%2C%5C%22ts%5C%22%3A64%2C%5C%22mode%5C%22%3A%5C%22ccm%5C%22%2C%5C%22adata%5C%22%3A%5C%22%5C%22%2C%5C%22cipher%5C%22%3A%5C%22aes%5C%22%2C%5C%22salt%5C%22%3A%5C%224d5i3s4avb6e0zfrA%3D%3D%3D%5C%22%2C%5C%22ct%5C%22%3A%5C%22kJwDrBcuHA9MQkZneuGac2g%2Bpg%3D%3D%5C%22%7D%22%2C%22crc%22%3A%5B1456649782307%2C1457243361344%2C1456172239357%2C1455699551544%2C1454868939948%2C1457629410864%2C1454195993821%2C1456905607301%5D%2C%22t%22%3A1456158840960%7D";
var y=decodeURIComponent(x);
//y="{"str":"{"iv":"wt5AsR8BtNteecathMxjnQ==","v":1,"iter":1000,"ks":256,"ts":64,"mode":"ccm","adata":"","cipher":"aes","salt":"4d5i3s4avb6e0zfrA===","ct":"kJwDrBcuHA9MQkZneuGac2g+pg=="}","crc":[1456649782307,1457243361344,1456172239357,1455699551544,1454868939948,1457629410864,1454195993821,1456905607301],"t":1456158840960}";
var z=JSON.parse(y);
//error in jsb: SyntaxError: JSON.parse: unexpected non-whitespace character after JSON data at line 1 column 4 of the JSON data

these code can work fine in web browser, but error in jsb at line with JSON.parse.

how to solve it?