next_char_info.js

require('es6-shim');

function next_char_info(str, pos) {
    var cp = str.codePointAt(pos);
    var size = cp > 0xFFFF ? 2 : 1;

    return {'cp': cp, 'size': size};
}

var str = '𠮷野家';
var length = str.length;
var pos = 0;
var info;

while (pos < length) {
    info = next_char_info(str, pos);
    console.log(str.substr(pos, info.size));
    pos += info.size;
}

string.js

require('es6-shim');
 
function MyString(str) {
    this.str = str;
    this.length = str.length;
 
    this.init = function() {
        this.pos = 0;
        this.cp = 0;
        this.size = 0;
        this.current = '';
    };
 
    this.init();
 
    this.next = function() {
 
    	if (this.pos >= this.length) {
            return false;
    	}
 
        this.cp = this.str.codePointAt(this.pos);
        this.size = this.cp > 0xFFFF ? 2 : 1;
        this.current = this.str.substr(this.pos, this.size);
        this.pos += this.size;
 
        return true;
    };

    this.move = function(pos) {
        this.pos = pos;
    }

    this.nextFrom = function(pos) {
        this.pos = pos;
        return this.next();
    }

    this.print_each_char = function() {
        this.init();
        while (this.next()) {
            console.log(this.current);
        }
    };
}
 
var str = new MyString('𠮷野家');
str.print_each_char();