JS custom with default value function _javascript tips

Starting to assume that it might be like PHP or Python.
JS Code

Copy Code code as follows:

function test (a,b= "er") {
Alert (a + B);
}

However, after the definition has been the error: missing objects. After the query found that JavaScript does not really define this, you can borrow ribs in arguments is a real parameter group, refer to the following example:
JS Code

Copy Code code as follows:

<script type= "Text/javascript" >
function Test (a) {
var B = arguments[1]? ARGUMENTS[1]: 50;
Return a + ': ' + b;
}
Alert (Test (5));
Alert (Test (5,9));
</script>

After the test, sure enough. It seems that everything has its own laws and cannot be taken for granted. Write it down here, lest you make a mistake again.