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
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’s called a self-invoked function. What you are doing when you call (function(){}) is returning a function object. When you append () to it, it is invoked and anything in the body is executed. The ; denotes the end of the statement, that’s why the 2nd invocation fails.
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
There isn’t any difference beyond the syntax. Regarding your concerns about the second method of doing it: Consider: (function namedfunc () { … }()) namedfunc will still not be in the global scope even though you provided the name. The same goes for anonymous functions. The only way to get it in that scope would … Read more
You need to bind d for each function created. One way to do that is to pass it as a parameter with a default value: lambda d=d: self.root.change_directory(d) Now the d inside the function uses the parameter, even though it has the same name, and the default value for that is evaluated when the function … Read more