JAVASCRIPT：我如何从外部访问这些 javascript 成员函数？

Question

I know how to access the below member function when it's written like this:

var blady_blah=
{
    some_member_function: function ()
    {
    }

}

I access it from outside doing blady_blah.some_member_function()

But how do I access the member function when it's written like this:

(function() {

    some_member_function: function ()
    {
    }

})();

Answer 1

Braces, { }, are used to define both object literals and function bodies. The difference is:

var name = {};    // Object literal

Which you may also see written as

var name = {

};

That's just the same but with some space in between so it's still an object literal, and unfortunately it looks very similar to:

var name = function () {    // Function body

};

An object can have members:

var name = {
  member: "string"
};

Whereas a function cannot; a function has statements:

var name = function () {
  do_something();
  var result = do_something_else();
};

You can't write

var name = function () {
  member: "string"
};

Because you've mixed the two uses of { } together.

A variable can be defined within a function, but it can't be seen outside the function - it's within the function scope:

var name = function () {
  var something_useful = string;
};

Answer 2

The second example is a closure (it just happens to have a syntax error inside). Minus the bad syntax, your self-evaluating anonymous function looks like this:

(function() {
})();

If you'd like, you can define functions inside this that will be invisible to the outside world. This is useful if you're interested in maintaining a clean global namespace, for example with library code.

(function() {
  function utilityFunctionFoo() {
  }

  function utilityFunctionBar() {
  }
})();

Of course, if you'd like to call any of these functions from the outside world, you're out of luck. Or are you? Actually, there's another way to define a function:

var foo = function() {
}

That's exactly the same as writing:

function foo() {
}

...Except that when written in the second style, you can actually omit the var keyword and create a global variable: Bringing it all together:

(function() {
  publicData = "stuff accessible from outside anonymous function";
  var privateData = "stuff that stays inside anonymous function";

  function utilityFunctionFoo() {
  }

  function utilityFunctionBar() {
  }


  usefulFunctionExport = function() {
    utilityFunctionFoo();
    utilityFunctionBar();
  }
})();

usefulFunctionExport();

Answer 3

You can't access it after the function it's in terminates. It's a local variable that goes out of scope when its parent function ends.

You should make the main function be a constructor so that it returns a new instance of a class (you could name it Blahdy_blah) with the member function as one of its properties.

Look up constructors, their return values, and accessing member variables.

Answer 4

If you want to execute the function you need to return an object that exposes the function.

var LIB = (function() {

    var fn = {
        member_function : function(){}
    };

    return fn;


})();

and to call

LIB.member_function();

Answer 5

(function() {

    blady_blah.some_member_function();

})();

If you need to add stuff into it you would write it like this.

(function() {

    blady_blah.some_member_function(function(){

        // Do stuff...

    });

})();