How to get the value in the span in special cases

How to get A?

The code copy is as follows:

<div>

<span>

A

<span>123</span>

</span>

</div>

<script type='text/javascript' src='./jquery-1.7.2.min.js'></script>

<script type='text/javascript'>

var a = $(".content")[0].firstChild.data;

function al(){

alert(a);

}

window.onload=al;

</script>