parseFloat的取值

<script type="text/javascript">

document.write(parseFloat("10")) 
document.write(parseFloat("10.00")) 
document.write(parseFloat("10.33")) 
document.write(parseFloat("34 45 66")) 
document.write(parseFloat(" 60 ")) 
document.write(parseFloat("40 years"))
document.write(parseFloat("He was 40"))

</script>
输出
10
10
10.33
34
60
40
NaN