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

You must test with #user element value not '#user' string

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