jquery Ajax uses the Get method to not upload values to the background, why

Title:
The following is the JS method
function Login () {
$.ajax ({
Type: "Get",
URL: ' valid.php ',
Data: "Username=admin",
DataType: "JSON",
Success:ajaxcomplete (Result),
Error:ajaxerror (response)});
});
}

Here are the valid.php
echo $_get[' username '];
?>

After triggering the login () method, the page error notice:undefined Index:username, meaning is not found this parameter, this is for what, solve!!

Reply to discussion (solution)

Data: "Username=admin", here is wrong or you data "username:admin"
or serialize it first.

You can't even write JS, how can you get the result?

function login () {  $.ajax ({    type: "Get",    URL: ' valid.php ',     data: "Username=admin",     dataType: " JSON ",     Success:ajaxcomplete,     error:ajaxerror  });}

Success and error require callback functions.
You either give the function a name, or you define the anonymous function directly

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