.interpolate method for formating jscript string

jscript-interpolate.js

String.prototype.replSubStr = function(startat, endat, replacement) {
    return this.substring(0, startat) + replacement + this.substring(endat+1);
}

String.prototype.interpolate = function() {
  var str = this.toString();
  var dict = new Object();
  if (arguments.length) {
    for(var k=0;k<arguments.length;k++) {
      if(typeof arguments[k] === "object") {
        for(var j in arguments[k]) {
          dict[j] = arguments[k][j];
        }
      } else {
        dict[k] = arguments[k];
      }
    }
  }
  var subs = new Array();
  for( var i=0; i<str.length-2;++i) {
    if(!(str.charAt(i)=='{' && str.charAt(i+1)!='{')){
      continue
    }
    for(var j=i+1; j<str.length;++j) {
      if(!(str.charAt(j)=='}' && str.charAt(j+1)!='}')){
        continue
      }
      token = str.substr(i+1,j-i-1);
      if (dict[token]!==undefined) {
        subs.push([i,j, dict[token]]);
        i = j;
      }
    }
  }
  while(subs.length){
    inst = subs.pop();
    str = str.replSubStr(inst[0],inst[1],inst[2]);
  }
  return str;
}

WScript.Echo("{0}! Are you {ok}! {{This}} will be ignored".interpolate('Hello',{'ok':'Okay','This':'That'}));