Answers for "$ not defined in javascript"

$ is not defined

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>

$ is not defined

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>

if not defined javascript

var a;
try {
    a = b + 1;  // throws ReferenceError if b is not defined
} 
catch (e) {
    a = 1;      // apply some default behavior in case of error
}
finally {
    a = a || 0; // normalize the result in any case
}

$ not defined error

<script src="http://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
<script type="text/javascript" src="./javascript.js"></script>
<script
    src="http://maps.googleapis.com/maps/api/js?key=YOUR_APIKEY&sensor=false">
</script>