javascript - Maintain this in a method passed by reference -

in following example, send parameter method "lostthis" object "instobj", "this" window object.

var obj = function() {}; obj.prototype.lostthis = function() {     console.log('lostthis', instanceof obj, this); };  var instobj = new obj;  var caller = {     runfn: function(fn) {         fn();     } };  caller.runfn(instobj.lostthis); 

console response:

lostthis false window 

run example

in following example (slightly more complex) there different ways call methods of "instobj" same , others can keep "this" object.

var obj = function() {};  obj.prototype.methodrefhasthis = function() {     var t = this;     return function() {         console.log('methodrefhasthis ', t instanceof obj, t);     }; };  obj.prototype.methodreflostthis = function() {     console.log('methodreflostthis ', instanceof obj, this); };  obj.prototype.methodrefmaybethis = function() {     console.log('methodrefmaybethis ', instanceof obj, this); };  var instobj = new obj; var caller = {     runfn: function(fn) {         fn();     } };  // width jquery $('button')     .bind('click', instobj.methodrefhasthis())     .bind('click', instobj.methodreflostthis);  caller.runfn(instobj.methodrefhasthis()); caller.runfn(instobj.methodreflostthis); caller.runfn(function() {     instobj.methodrefmaybethis(); });​ 

console response:

methodrefhasthis  true obj methodreflostthis  false window methodrefmaybethis  true obj  methodrefhasthis  true obj methodreflostthis  false <button>​press here​</button>​ 

run example

i understand happens jquery assign method event, could call method "methodreflostthis" no lose "this" object passed reference?

thanks

solution @am_not_i_am , @dan_davies_brackett , @ben_lee

var obj = function() {}; obj.prototype.lostthis = function() {     console.log('lostthis', instanceof obj, this); };  var instobj = new obj;  var caller = {     runfn: function(fn) {         fn();     } };  caller.runfn(instobj.lostthis.bind(instobj)); caller.runfn($.proxy(instobj.lostthis, instobj)); 

console response:

lostthis true obj lostthis true obj   ​ 

run example

if don't want use 1 of techniques you've found work, can use function.prototype.bind bind calling context new function...

caller.runfn(instobj.lostthis.bind(instobj)); 

this returns new function when invoked, set calling context whatever passed first argument .bind().

any additional arguments passed .bind() set fixed arguments returned function.