Why split the script tag when writing it with document write

Question

Why do some sites  or advertisers that give clients javascript code  employ a technique of splitting the  lt script gt  and or  lt  script gt  tags up within document write   calls   I noticed that Amazon does this as well  for example    lt script type  text javascript  gt    if  typeof window  jQuery       undefined   document write   lt scr   ipt type  text javascript  src  http   z-ecx images-amazon com images G 01 javascripts lib jquery jquery-1 2 6 pack  V265113567  js  gt  lt  sc   ript gt      lt  script gt

User · Answer

Here s another variation I ve used when wanting to generate a script tag inline  so it executes immediately  without needing any form of escapes    lt script gt      var script   document createElement  script        script src     path to script js       document write script outerHTML    lt  script gt     Note  contrary to most examples on the net  I m not setting type  text javascript  on neither the enclosing tag  nor the generated one  there is no browser not having that as the default  and so it is redundant  but will not hurt either  if you disagree

User · Answer

The  lt  script gt  inside the Javascript string litteral is interpreted by the HTML parser as a closing tag  causing unexpected behaviour  see example on JSFiddle    To avoid this  you can place your javascript between comments  this style of coding was common practice  back when Javascript was poorly supported among browsers   This would work  see example in JSFiddle     lt script type  text javascript  gt       lt  --     if  jQuery     undefined            document write   lt script type  text javascript  src  http   z-ecx images-amazon com images G 01 javascripts lib jquery jquery-1 2 6 pack  V265113567  js  gt  lt  script gt                  -- gt   lt  script gt       but to be honest  using document write is not something I would consider best practice  Why not manipulating the DOM directly    lt script type  text javascript  gt       lt  --     if  jQuery     undefined            var script   document createElement  script            script setAttribute  type    text javascript            script setAttribute  src    http   z-ecx images-amazon com images G 01 javascripts lib jquery jquery-1 2 6 pack  V265113567  js            document body appendChild script                -- gt   lt  script gt

User · Answer

I think is for prevent the browser s HTML parser from interpreting the  lt script gt   and mainly the   lt  script gt  as the closing tag of the actual script  however I don t think that using document write is a excellent idea for evaluating script blocks  why don t use the DOM     var newScript   document createElement  script

User · Answer

lt  script gt  has to be broken up because otherwise it would end the enclosing  lt script gt  lt  script gt  block too early  Really it should be split between the  lt  and the    because a script block is supposed  according to SGML  to be terminated by any end-tag open  ETAGO  sequence  i e   lt         Although the STYLE and SCRIPT elements use CDATA for their data model  for these elements  CDATA must be handled differently by user agents  Markup and entities must be treated as raw text and passed to the application as is  The first occurrence of the character sequence   lt     end-tag open delimiter  is treated as terminating the end of the element s content  In valid documents  this would be the end tag for the element    However in practice browsers only end parsing a CDATA script block on an actual  lt  script gt  close-tag   In XHTML there is no such special handling for script blocks  so any  lt   or  amp   character inside them must be  amp escaped  like in any other element  However then browsers that are parsing XHTML as old-school HTML will get confused  There are workarounds involving CDATA blocks  but it s easiest simply to avoid using these characters unescaped  A better way of writing a script element from script that works on either type of parser would be    lt script type  text javascript  gt      document write   x3Cscript type  text javascript  src  foo js  gt  x3C script gt      lt  script gt

User · Answer

The solution Bobince posted works perfectly for me  I wanted to offer an alternative method as well for future visitors   if  typeof jQuery      undefined          function             var sct   document createElement  script            sct src     https      document location protocol    https     http                   ajax googleapis com ajax libs jquery 1 10 1 jquery min js           sct type    text javascript           sct async    true           var domel   document getElementsByTagName  script   0           domel parentNode insertBefore sct  domel                 In this example  I ve included a conditional load for jQuery to demonstrate use case  Hope that s useful for someone

User · Answer

The  lt  script gt  inside the Javascript string litteral is interpreted by the HTML parser as a closing tag  causing unexpected behaviour  see example on JSFiddle    To avoid this  you can place your javascript between comments  this style of coding was common practice  back when Javascript was poorly supported among browsers   This would work  see example in JSFiddle     lt script type  text javascript  gt       lt  --     if  jQuery     undefined            document write   lt script type  text javascript  src  http   z-ecx images-amazon com images G 01 javascripts lib jquery jquery-1 2 6 pack  V265113567  js  gt  lt  script gt                  -- gt   lt  script gt       but to be honest  using document write is not something I would consider best practice  Why not manipulating the DOM directly    lt script type  text javascript  gt       lt  --     if  jQuery     undefined            var script   document createElement  script            script setAttribute  type    text javascript            script setAttribute  src    http   z-ecx images-amazon com images G 01 javascripts lib jquery jquery-1 2 6 pack  V265113567  js            document body appendChild script                -- gt   lt  script gt

User · Answer

I think is for prevent the browser s HTML parser from interpreting the  lt script gt   and mainly the   lt  script gt  as the closing tag of the actual script  however I don t think that using document write is a excellent idea for evaluating script blocks  why don t use the DOM     var newScript   document createElement  script

User · Answer

Here s another variation I ve used when wanting to generate a script tag inline  so it executes immediately  without needing any form of escapes    lt script gt      var script   document createElement  script        script src     path to script js       document write script outerHTML    lt  script gt     Note  contrary to most examples on the net  I m not setting type  text javascript  on neither the enclosing tag  nor the generated one  there is no browser not having that as the default  and so it is redundant  but will not hurt either  if you disagree

User · Answer

The solution Bobince posted works perfectly for me  I wanted to offer an alternative method as well for future visitors   if  typeof jQuery      undefined          function             var sct   document createElement  script            sct src     https      document location protocol    https     http                   ajax googleapis com ajax libs jquery 1 10 1 jquery min js           sct type    text javascript           sct async    true           var domel   document getElementsByTagName  script   0           domel parentNode insertBefore sct  domel                 In this example  I ve included a conditional load for jQuery to demonstrate use case  Hope that s useful for someone

User · Answer

I think is for prevent the browser s HTML parser from interpreting the  lt script gt   and mainly the   lt  script gt  as the closing tag of the actual script  however I don t think that using document write is a excellent idea for evaluating script blocks  why don t use the DOM     var newScript   document createElement  script

User · Answer

lt  script gt  has to be broken up because otherwise it would end the enclosing  lt script gt  lt  script gt  block too early  Really it should be split between the  lt  and the    because a script block is supposed  according to SGML  to be terminated by any end-tag open  ETAGO  sequence  i e   lt         Although the STYLE and SCRIPT elements use CDATA for their data model  for these elements  CDATA must be handled differently by user agents  Markup and entities must be treated as raw text and passed to the application as is  The first occurrence of the character sequence   lt     end-tag open delimiter  is treated as terminating the end of the element s content  In valid documents  this would be the end tag for the element    However in practice browsers only end parsing a CDATA script block on an actual  lt  script gt  close-tag   In XHTML there is no such special handling for script blocks  so any  lt   or  amp   character inside them must be  amp escaped  like in any other element  However then browsers that are parsing XHTML as old-school HTML will get confused  There are workarounds involving CDATA blocks  but it s easiest simply to avoid using these characters unescaped  A better way of writing a script element from script that works on either type of parser would be    lt script type  text javascript  gt      document write   x3Cscript type  text javascript  src  foo js  gt  x3C script gt      lt  script gt

User · Answer

lt  script gt  has to be broken up because otherwise it would end the enclosing  lt script gt  lt  script gt  block too early  Really it should be split between the  lt  and the    because a script block is supposed  according to SGML  to be terminated by any end-tag open  ETAGO  sequence  i e   lt         Although the STYLE and SCRIPT elements use CDATA for their data model  for these elements  CDATA must be handled differently by user agents  Markup and entities must be treated as raw text and passed to the application as is  The first occurrence of the character sequence   lt     end-tag open delimiter  is treated as terminating the end of the element s content  In valid documents  this would be the end tag for the element    However in practice browsers only end parsing a CDATA script block on an actual  lt  script gt  close-tag   In XHTML there is no such special handling for script blocks  so any  lt   or  amp   character inside them must be  amp escaped  like in any other element  However then browsers that are parsing XHTML as old-school HTML will get confused  There are workarounds involving CDATA blocks  but it s easiest simply to avoid using these characters unescaped  A better way of writing a script element from script that works on either type of parser would be    lt script type  text javascript  gt      document write   x3Cscript type  text javascript  src  foo js  gt  x3C script gt      lt  script gt

User · Answer

I think is for prevent the browser s HTML parser from interpreting the  lt script gt   and mainly the   lt  script gt  as the closing tag of the actual script  however I don t think that using document write is a excellent idea for evaluating script blocks  why don t use the DOM     var newScript   document createElement  script

User · Answer

lt  script gt  has to be broken up because otherwise it would end the enclosing  lt script gt  lt  script gt  block too early  Really it should be split between the  lt  and the    because a script block is supposed  according to SGML  to be terminated by any end-tag open  ETAGO  sequence  i e   lt         Although the STYLE and SCRIPT elements use CDATA for their data model  for these elements  CDATA must be handled differently by user agents  Markup and entities must be treated as raw text and passed to the application as is  The first occurrence of the character sequence   lt     end-tag open delimiter  is treated as terminating the end of the element s content  In valid documents  this would be the end tag for the element    However in practice browsers only end parsing a CDATA script block on an actual  lt  script gt  close-tag   In XHTML there is no such special handling for script blocks  so any  lt   or  amp   character inside them must be  amp escaped  like in any other element  However then browsers that are parsing XHTML as old-school HTML will get confused  There are workarounds involving CDATA blocks  but it s easiest simply to avoid using these characters unescaped  A better way of writing a script element from script that works on either type of parser would be    lt script type  text javascript  gt      document write   x3Cscript type  text javascript  src  foo js  gt  x3C script gt      lt  script gt

[javascript] Why split the <script> tag when writing it with document.write()?

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