strtotime in js code example
Example: strtotime in javascript
You need to use the same time-zone for a same comparison:
echo strtotime("2011-01-26 13:51:50 GMT");
// 1296049910
var d = Date.parse("2011-01-26 13:51:50 GMT") / 1000;
console.log(d);
// 1296049910