I want to create a closure dynamically. See code below for explanation.
function myFunction(){
parentScopedVar(); //Would like to be able to call without using 'this'.
}
function myDynamicFunc(dynamicClosure){
//What do I need to do here to dynamically create
//a var called 'parentScopedVar' that can be referenced from myFunction?
myFunction.call(self);
}
myDynamicFunc(
{
parentScopedVar : function() { alert('Hello World'); }
});
Javascript uses lexical scope (based on where the code is declared), not dynamic scope.
If you are determined to try to do something that the language doesn't really encourage, you can force a string of code to be evaluated in your current execution context using eval(string of code here). In fact, you can do all sorts of odd things with eval(), but I'd much rather write code in a way that leverages the strengths of Javascript than to use a coding style that goes against the main design theme of the language (that's my opinion).
It's not entirely clear to me what problem you're trying to solve, but you can just pass a function as an argument and then call it via the argument from the called function.
// declare your function that takes a function reference an argument
function myFunction(callback) {
// call the function that was passed
callback();
}
function myDynamicFunc(){
// declare a local function
function myAlert() {
alert('Hello World');
}
// call your other function and pass it any function reference
myFunction(myAlert);
}
This will not pass an entire execution context. To do that, you'd have to package up the context in an object and pass a reference to the object, then dereference the properties from the object. That is typically how you pass an environment in JS.
You can use locally declared functions to provide access to parent scope from a callback (again lexical scope):
// declare your function that takes a function reference an argument
function doSomething(callback) {
// call the function that was passed
callback();
}
function myFunc() {
var myLocal1 = "Hello";
var myLocal2 = "World";
function callback() {
// when this is called, it has access to the variables of the parent scope
alert(myLocal1 + " " + myLocal2);
}
doSomething(myFunc);
}
You can even use it as a lasting closure:
// declare your function that takes a function reference an argument
function doSomething(callback) {
// call the function that was passed
callback();
}
function myFunc() {
var myLocal1 = "Hello";
var myLocal2 = "World";
function callback() {
// when this is called, it has access to the variables of the parent scope
// which are still alive in this closure even though myFunc has finished
// executing 10 minutes ago
alert(myLocal1 + " " + myLocal2);
}
// call the callback function 10 minutes from now,
// long after myFunc has finished executing
setTimeout(callback, 10 * 60 * 1000);
}
Here are some reference articles on lexical and dynamic scope in Javascript:
Is it possible to achieve dynamic scoping in JavaScript without resorting to eval?
Are variables statically or dynamically "scoped" in javascript?
