JavaScript scope and closure

by

The point of this is that any variables declared in the cool stuff will not be created in global namespace. Any function in javascript will create such a scope. Suppose you have some javascript you want to run. If you do this:

var b = 1; 
// stuff using b

And some other code uses b, it will get your left over value. (Or, even worse, if some other code sets b before your code runs, then tries to get its old value later, you’d have changed it in the meantime.)

On the other hand, if you have this code, which declares and then calls the a function:

function a() { 
     var b = 1;
}

a();

And some other code later on uses b, it will not see your values, since b is local to the function. The problem with this, of course, is that you’re still making a global name – “a”, in this case. So, we want a function with no name – this is why you get the code you described. It declares a function with no name, and then calls it.

Unfortunately, you can’t just say:

function() { ... }()

because this will be parsed as a function declaration statement, and then a syntax error. By wrapping the function declaration in parenthesis, you get a function expression, which can then be called. You call it like any other function expression (like a, above), using the second set of parens. For example, if the function took arguments, you’d pass them there:

(function(a) { ... })(1)

More Related Contents:

  1. How do JavaScript closures work?
  2. var self = this?
  3. JavaScript closures vs. anonymous functions
  4. Is it possible to gain access to the closure of a function?
  5. Please explain the use of JavaScript closures in loops [duplicate]
  6. What underlies this JavaScript idiom: var self = this?
  7. JavaScript variable binding and loop
  8. Is window really global in Javascript?
  9. JavaScript Variable Scope [duplicate]
  10. javascript closure immediate evaluation [duplicate]
  11. dynamically call local function in javascript
  12. I would like to ask how to explain this (javascript function)
  13. What’s the difference between using “let” and “var”?
  14. What is the purpose of a self executing function in javascript?
  15. JavaScript function aliasing doesn’t seem to work
  16. Assigning prototype methods *inside* the constructor function – why not?
  17. Function declarations inside if/else statements?
  18. Doesn’t JavaScript support closures with local variables? [duplicate]
  19. Javascript Closures and ‘this’
  20. How do I pass the this context to a function?
  21. ECMAScript 2015: const in for loops
  22. What is the difference between “let” and “var”?
  23. javascript – How to make this code work? [duplicate]
  24. Access a variable outside the scope of a Handlebars.js each loop
  25. Is there a performance difference between ‘let’ and ‘var’ in JavaScript
  26. Example of a circular reference in Javascript?
  27. What exactly does “closure” refer to in JavaScript?
  28. Why does IE nuke window.ABC variables?
  29. Scope issues with Angular UI modal
  30. Passing a function with arguments as an argument?

Leave a Comment