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I am new to underscore.js. What is the purpose of [context] in _.each() ? How should it be used? The context parameter just sets the value of this in the iterator function. var someOtherArray = ["name","patrick","d","w"]; _.each([1, 2, 3], function(num) { // In here, "this" refers to the same Array as "someOtherArray" alert( this[num] ); // num is the value from the array being iterated // so this[num] gets the item at the "num" index of // someOtherArray. }, someOtherArray); Working Example: http://jsfiddle.net/a6Rx4/ It uses the number from each member of the Array being iterated to get the

Explanation to why this is not a duplicate: My code is already working, I have included as a comment. The question is why the this context change when I include it to click handler function. I'm attempting a calculator project in React. The goal is to attach onclick handlers to number buttons so the numbers are displayed on the calculator display area. If the handler is written directly to render method it is working, however, if I'm trying from the ComponentDidMount I get an error this.inputDigit is not a function . How do I bind this.inputDigit(digit) properly? import React from 'react';

Using the method .attachEvent() in IE, how can I reference the caller object (the element that triggered the event) with this ? In normal browsers, using .addEventListener , the var this points to the element, while in IE it points to the window object. I need it to work with the following code: var element = //the element, doesn't matter how it is obtained element.addAnEvent = function(name, funct){ if(element.addEventListener) // Works in NORMAL browsers... else if(element.attachEvent){ element.attachEvent("on"+name, funct); //where the value of "this" in funct should point to "element" } }

Can anybody explain to me why A is true and B is false? I would have expected B to be true as well. function MyObject() { }; MyObject.prototype.test = function () { console.log("A", this instanceof MyObject); (function () { console.log("B", this instanceof MyObject); }()); } new MyObject().test(); this is special. It refers to the object that the function is being called on behalf of (most commonly via dot syntax). So, in the case of A , the function is being called on behalf of a new MyObject object. B is in a different function that isn't explicitly being called on behalf of any object, so

I'm sure there's a simple answer to this, but it's Friday afternoon and I'm tired. :( Not sure how to explain it, so I'll just go ahead and post example code... Here is a simple object: var Bob = { Stuff : '' , init : function() { this.Stuff = arguments[0] } , doSomething : function() { console.log( this.Stuff ); } } And here it is being used: $j = jQuery.noConflict(); $j(document).ready( init ); function init() { Bob.init('hello'); Bob.doSomething(); $j('#MyButton').click( Bob.doSomething ); } Everything works, except for the last line. When jQuery calls the doSomething method it is

The behavior of "this" when function bar is called is baffling me. See the code below. Is there any way to arrange for "this" to be a plain old js object instance when bar is called from a click handler, instead of being the html element? // a class with a method function foo() { this.bar(); // when called here, "this" is the foo instance var barf = this.bar; barf(); // when called here, "this" is the global object // when called from a click, "this" is the html element $("#thing").after($("<div>click me</div>").click(barf)); } foo.prototype.bar = function() { alert(this); } Aaron Qian Welcome

I'm using webkitRequestAnimationFrame but I'm having trouble using it inside of an object. If I pass the this keyword it will use window and I can't find a way for it to use the specified object instead. Example: Display.prototype.draw = function(){ this.cxt.clearRect(0, 0, this.canvas.width, this.canvas.height); //Animation stuff here. window.webkitRequestAnimationFrame(this.draw); }; I have also tried this but to no avail: Display.prototype.draw = function(){ this.cxt.clearRect(0, 0, this.canvas.width, this.canvas.height); //Animation stuff here. var draw = this.draw; window