Difference between revisions of "Porting from FPC/Delphi to pas2js"
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JavaScript enforces an absolute async manner of programming: | JavaScript enforces an absolute async manner of programming: | ||
| − | *Many calls are asynchronous and return immediately | + | *Many calls are asynchronous and return immediately. For example loading a resource. |
*There is '''no''' Application.ProcessMessages. You cannot wait till some event occurs. You must set an event. That's why anonymous functions are so frequently used in JS - they keep the local variables accessible. | *There is '''no''' Application.ProcessMessages. You cannot wait till some event occurs. You must set an event. That's why anonymous functions are so frequently used in JS - they keep the local variables accessible. | ||
*There is no multithreading, no shared memory. Many browsers/JS engines allow to start workers, but that is more like processes than threads. | *There is no multithreading, no shared memory. Many browsers/JS engines allow to start workers, but that is more like processes than threads. | ||
| + | |||
| + | =Details= | ||
| + | |||
| + | A more detailed list can be found in the [https://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/utils/pas2js/docs/translation.html?view=co translation.html].file in the sources. | ||
Revision as of 14:54, 21 February 2019
This page contains useful tips for Delphians and FPC users on how to port code to pas2js.
Numbers
- Internally all numbers are double
- There is no Int64 and no QWord
- All bitwise operators are limited to 32bit, including the mod operator, which is limited to signed 32bit.
- Integers overflows' at runtime differ from Delphi/FPC. For example adding var i: byte = 200; ... i:=i+100; will result in i=300 instead of i=44 as in Delphi/FPC. When range checking {$R+} is enabled i:=300 will raise an ERangeError.
- Division by zero does not raise EDivByZero, instead it results in NaN.
Strings
- String is UnicodeString and there are no other string types.
- Strings are immutable in JS. That means changing a single character creates a new string. That's why some fast Delphi/FPC string functions are much slower in pas2js.
Asynchronous vs Waiting
JavaScript enforces an absolute async manner of programming:
- Many calls are asynchronous and return immediately. For example loading a resource.
- There is no Application.ProcessMessages. You cannot wait till some event occurs. You must set an event. That's why anonymous functions are so frequently used in JS - they keep the local variables accessible.
- There is no multithreading, no shared memory. Many browsers/JS engines allow to start workers, but that is more like processes than threads.
Details
A more detailed list can be found in the translation.html.file in the sources.
