Cannot be called after mobile Window.prototype

I am in init.js
Window.prototype.interface = function () {

return "https://xxx.xxxxxxx.com"

}
/ /
Window.prototype.getParam=function (paramName) {

var paramValue = "", isFound = !1;
if (this.location.search.indexOf("?") == 0 && this.location.search.indexOf("=") > 1) {
    var arrSource = unescape(this.location.search).substring(1, this.location.search.length).split("&"), i = 0;
    while (i < arrSource.length && !isFound) arrSource[i].indexOf("=") > 0 && arrSource[i].split("=")[0].toLowerCase() == paramName.toLowerCase() && (paramValue = arrSource[i].split("=")[1], isFound = !0), iPP
}
return paramValue == "" && (paramValue = null), paramValue

}
wrote two methods
, but after the introduction of init.js, the
page window.getParam can get the value
window.interface is undefined
what is the reason

Window.prototype.publicMethod= {

interface:"",
getParam:function(){}

}

same thing
Please answer