<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>第一个javascript计算页面</title></head><body><script type="text/javascript"> var s1="abc"; alert(typeof s1); alert(s1.length); var s2=new String("def"); alert(typeof s2); alert(s2.length); /*String.prototype.getLength=function () { return this.getLength(); } var l1=s1.getLength(); alert(l1); var l2=s2.getLength(); alert(l2);*/ alert("abcdf".charAt(0));//a alert("sunyuhuan".substr(2,3));//nyu alert("sunyuhuan".substring(2,3));//n</script></html>
来源：https://www.cnblogs.com/god1/p/12114239.html