When you assign the function to the click handler, a closure is created. Basically a closure is formed when you nest functions, inner functions can refer to the variables present in their outer enclosing functions even after their parent functions have already executed. At the time that the click event is executed, the handler refers … Read more
It’s because, until ECMAscript 262 edition 5, there was a big confusion if people who where using the constructor pattern, forgot to use the new keyword. If you forgot to use new when calling a constructor function in ES3, this referenced the global object (window in a browser) and you would clobber the global object … Read more
You can’t. You have to use a named function or store the reference somehow. var handler; function doSomethingWith(param) { handler = function(){ document.write(param); }; document.body.addEventListener(‘scroll’, handler,false); } setTimeout(function() { document.body.removeEventListener(‘scroll’, handler ,false); }, 3000); The best would be to do this in a structured way, so that you can identify different handlers and remove them. … Read more
if you are inside the actual function, you can use arguments.callee as a reference to the function. as in: button.addEventListener(‘click’, function() { ///this will execute only once alert(‘only once!’); this.removeEventListener(‘click’, arguments.callee); }); EDIT: This will not work if you are working in strict mode (“use strict”;)
Anonymous class instance — is it a bad idea? Yes, a very bad one. Just as bad as new function() { … } was in ES5. This writing style leads to the creation of a new constructor function and prototype object every time the expression is evaluated. If you create multiple objects with this approach, … Read more
No. JSON is purely meant to be a data description language. As noted on http://www.json.org, it is a “lightweight data-interchange format.” – not a programming language. Per http://en.wikipedia.org/wiki/JSON, the “basic types” supported are: Number (integer, real, or floating point) String (double-quoted Unicode with backslash escaping) Boolean (true and false) Array (an ordered sequence of values, … Read more
Drop the semicolon after the function definition. (function (msg){alert(msg)}) (‘SO’); Above should work. DEMO Page: https://jsfiddle.net/e7ooeq6m/ I have discussed this kind of pattern in this post: jQuery and $ questions EDIT: If you look at ECMA script specification, there are 3 ways you can define a function. (Page 98, Section 13 Function Definition) 1. Using … Read more
In the case of the anonymous function expression, the function is anonymous — literally, it has no name. The variable you’re assigning it to has a name, but the function does not. (Update: That was true through ES5. As of ES2015 [aka ES6], often a function created with an anonymous expression gets a true name [but … Read more
It doesn’t work because it is being parsed as a FunctionDeclaration, and the name identifier of function declarations is mandatory. When you surround it with parentheses it is evaluated as a FunctionExpression, and function expressions can be named or not. The grammar of a FunctionDeclaration looks like this: function Identifier ( FormalParameterListopt ) { FunctionBody … Read more
They’re virtually the same. The first wraps parentheses around a function to make it a valid expression and invokes it. The result of the expression is undefined. The second executes the function and the parentheses around the automatic invocation make it a valid expression. It also evaluates to undefined. I don’t think there’s a “right” … Read more