What's wrong with this javascript code?

The error message returned when the javascript code is incorrect. The answer is "select all". the code is as follows: HTMLcode & lt; html & gt; & lt; body & gt; & lt; script & gt; what is wrong with this javascript code?
The select all function is invalid:
The code is as follows:

HTML code

        Script document. write ("
  
  

   
   
"); For (var I = 0; I <20; I ++) {document. write ("
   
   
"); Document. write ('Heihei'); document. write ("
");} Document. write ("
  
  
"); ScriptSelect all scripts var cnames = document. getElementsByName ("arr []"); alert (cnames. length); function all (obj) {for (var I = 0; I
  

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Use firebug and debug it.
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It is best to use Firefox firbug debugging in js.
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All is a reserved JavaScript word and cannot be used as a function name.
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Discussion
Var cnames = document. getElementsByName ("arr []");

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Discussion

All is a reserved JavaScript word and cannot be used as a function name.