64bit int differences between .NET and javascript

I'm passing a long int from C# (DateTime.Now().Ticks) to a web page then trying to pass it back for the sake of concurrency.

634290758865783994 becomes 634290758865783900

Why is this? I t开发者_高级运维hought both the System.Long and Javascript Number were 64 bit integers.

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ECMAScript (the formal name for javascript) stores numbers as IEEE-754 double precision floating-points.

These can only represent the values up to 2^53 using the significant bits, and everything above this will be an approximation.