How to prevent non-alphanumeric input in javascript?

Question

$(\"#user\").keyup(function(e){ 
    var regx = /^[A-Za-z0-9]+$/;
    if (!regx.test(\'#user\')) 
    {$(\"#infoUser\").html(\"Alphanumeric only allowed !\");}
);}
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Answer 1

THis line

regx.test('#user')

has you testing the string #user, and that is a string that has a bad character (the #). So it will always say not allowed.

Use the actual value of your $("#user") there by using $(this).val()