当在字符序列的末尾添加空格时，为什么此RegEx失败？

Question

Here's some code that I've got in my javascript to detect whether or not a string is a Right-To-Left (RTL) script:

is_right_to_left : function (text) {

      /*
       * Right-to-left Unicode blocks for modern scripts are:
       *
       * Consecutive range of the main letters:
       * U+0590  to U+05FF  - Hebrew
       * U+0600  to U+06FF  - Arabic
       * U+0700  to U+074F  - Syriac
       * U+0750  to U+077F  - Arabic Supplement
       * U+0780  to U+07BF  - Thaana
       * U+07C0  to U+07FF  - N'Ko
       * U+0800  to U+083F  - Samaritan
       *
       * Arabic Extended:
       * U+08A0  to U+08FF  - Arabic Extended-A
       *
       * Consecutive presentation forms:
       * U+FB1D  to U+FB4F  - Hebrew presentation forms
       * U+FB50  to U+FDFF  - Arabic presentation forms A
       *
       * More Arabic presentation forms:
       * U+FE70  to U+FEFF  - Arabic presentation forms B
       */

        var ltrChars        = 'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590\u0800-\u1FFF'+'\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF',
            rtlChars        = '\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC',
            rtlDirCheck     = new RegExp('^[^'+ltrChars+']*['+rtlChars+']');

        return rtlDirCheck.test(text);

    }

This is working up to all the tests I've done. However, if I add a space to some sequences of characters from an RTL script, it fails the test. For example, if I have ﺮﺳﻷﺍ the function correctly detects that the string is RTL. However, if I add a trailing space then the function reports that it is NOT an RTL script. What is wrong with my RegEx? I want to be sure that a space won't throw it off. Any ideas?

Answer 1

I don't want a space anywhere to throw it off, not just at the end. How can I achieve that?

You want to use a negative look ahead operator.

 function is_right_to_left (text) { /* * Right-to-left Unicode blocks for modern scripts are: * * Consecutive range of the main letters: * U+0590 to U+05FF - Hebrew * U+0600 to U+06FF - Arabic * U+0700 to U+074F - Syriac * U+0750 to U+077F - Arabic Supplement * U+0780 to U+07BF - Thaana * U+07C0 to U+07FF - N'Ko * U+0800 to U+083F - Samaritan * * Arabic Extended: * U+08A0 to U+08FF - Arabic Extended-A * * Consecutive presentation forms: * U+FB1D to U+FB4F - Hebrew presentation forms * U+FB50 to U+FDFF - Arabic presentation forms A * * More Arabic presentation forms: * U+FE70 to U+FEFF - Arabic presentation forms B */ var ltrChars = 'A-Za-z\\\À-\\\Ö\\\Ø-\\\ö\\\ø-\\\ʸ\\\̀-\\\֐\\\ࠀ-\\\῿'+'\\\Ⰰ-\\\﬜\\\﷾-\\\﹯\\\﻽-\\\￿', rtlChars = '\\\֑-\\\߿\\\יִ-\\\﷽\\\ﹰ-\\\ﻼ', rtlDirCheck = new RegExp('^(?!.*['+ltrChars+'\\\\s]+.*)['+rtlChars+']$'); return rtlDirCheck.test(text); } alert(is_right_to_left("ﺮﺳﻷ ﺍ")); 

Here is a quick description of the regex: