js prototype intercepts string function_javascript skills

String.prototype.strLen = function() {
var len = 0;
for (var i = 0; i < this.length; i ) {
if (this.charCodeAt(i) > 255 || this.charCodeAt(i) < 0) len = 2; else len ;
}
return len;
}
//Split the string into characters and store them in the array
String.prototype.strToChars = function(){
var chars = new Array();
for (var i = 0; i < this.length; i ){
chars[i] = [this.substr(i, 1), this.isCHS(i)];
}
String.prototype.charsArray = chars;
return chars;
}
//Determine whether a character is a Chinese character
String.prototype.isCHS = function(i){
if (this.charCodeAt(i) > 255 || this.charCodeAt(i) < 0)
return true;
else
return false;
}
//Intercept string (from start byte to end byte)
String.prototype.subCHString = function(start, end){
var len = 0;
var str = "";
this.strToChars( );
for (var i = 0; i < this.length; i ) {
if(this.charsArray[i][1])
len = 2;
else
len ;
if (end < len)
return str;
else if (start < len)
str = this.charsArray[i][0];
}
return str;
}
//Intercept string (intercept length bytes from start byte)
String.prototype.subCHStr = function(start, length){
return this. subCHString(start, start length);
}
var li= document.getElementsByName("listtitle");
for(var i=0;i{
li[i].innerHTML=li[i].innerHTML.subCHStr(0,28) "...";
}