PHP text box

PHP text box problems have just been learned, PHP, encountered a lot of problems, please kindly help solve! 1. value = & quot; content & quot; already exists in the text box. how can I click a button to clear the content in the text box or use other content to replace the existing content. how can I select another PHP text box in a drop-down menu?
I just learned PHP and encountered many problems. please help me solve them!

1. the text box already contains value = "content". how can I click a button to clear the content in the text box or use other content to replace the existing content?

2. how to select a value from a drop-down menu? the corresponding content will be displayed in the other text box.
For example, when selecting 1, the text box displays 2
When selecting 2, the text box displays 2

Please kindly advise. if you have any code, send one.

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It should be a javascript issue.
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Document. getElementById ('test'). value = 'empty content box '; // clear
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Function delSearch (svalue) {// reloads the window if Nav4 resized
Var searchkey = document. getElementById ("searchKey ");
If (searchkey. value = svalue ){
Searchkey. value = '';
}
}
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Js implementation
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... There is a button in the html for clearing.

HTML code

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   Discussion
   
... There is a button in the html for clearing.
   

   
HTML code
   

   
   

   

   

   

   
2nd people forget how code is represented,
   

   
You only need to assign the value from the drop-down box to the php text box, and then display the text box.
   

  
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..........
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   Discussion
   
Function delSearch (svalue) {// reloads the window if Nav4 resized
   
Var searchkey = document. getElementById ("searchKey ");
   
If (searchkey. value = svalue ){
   
Searchkey. value = '';
   
}
   
}
   

  
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Onclick = "reset ()"