Setting a variable in the closure scope

问题

I think I understand why variables exist outside of the function they were declared in, because you're returning another function:

myFunction = function() {
    var closure = 'closure scope'
    return function() {
        return closure;
    }
}
A = myFunction(); // myFunction returns a function, not a value
B = A(); // A is a function, which when run, returns:
console.log(B); // 'closure scope'

The way that it's written now, calling A() is like a getter.

Q: How can I write myFunction so that calling A(123) is a setter?

回答1:

Try the following:

myFunction = function() {
    var closure = 'closure scope'

    // value is optional
    return function(value) {
        // if it will be omitted
        if(arguments.length == 0) {
            // the method is a getter
            return closure;
        } else {
            // otherwise a setter
            closure = value;
            // with fluid interface ;)
            return this;
        }
    }
}
A = myFunction(); // myFunction returns a function, not a value
A(123); // set value
B = A(); // A is a function, which when run, returns:
console.log(B); // '123'

回答2:

You could do something like this if you want both getter and setter for example:

var func = function() {
  var closure = 'foo';

  return {
    get: function() { return closure; },
    set: function(value) { closure = value; }
  }
};

var A = func();

A.set('foobar');
console.log(A.get()); //=> "foobar"

回答3:

Should be as simple as:

myFunction = function() {
    var closure = 'closure scope'
    return function(setTo) {
        if (typeof setTo !== "undefined") {
            closure = setTo;
            return this; //support call chaining, good idea hek2mgl
        } else {
            return closure;
        }
    }
}

Since the closure variable is within the closure of the function's scope, you should be able to assign to it the same way you can read from it.

See jsFiddle: http://jsfiddle.net/WF4VT/1/

回答4:

Another alternative would be to use a class and define getters and setters:

function MyClass(p){
    this._prop = p;
}
MyClass.prototype = {
    constructor: MyClass,
    get prop(){
        return this._prop;
    },
    set prop(p){
        this._prop = p;
    }
}

var myObject = new MyClass("TEST");
console.log(myObject.prop);
myObject.prop = "test";
console.log(myObject.prop);

Demo: http://jsfiddle.net/louisbros/bMkbE/

回答5:

jsFiddle Demo

Have your returned function accept an argument. Use it as a setter:

myFunction = function() {
 var closure = 'closure scope';
 return function(val) {
    closure = val;
    return closure;
 }
}
A = myFunction(); // myFunction returns a function, not a value
B = A(123); // A is a function, which when run, returns:
console.log(B); // 'closure scope'

回答6:

Revisiting this question, I see that I could do it this way:

    function outside() {
    	var result = 'initialized'
    	return inside
    	function inside(argVariable) {
    		if(arguments.length) {
    			result = argVariable
    			return this
    		} else {
    			return result
    		}
    	}
    }
    myFunction = outside() // outside returns a function
    X = myFunction() // returns: 'initialized'
    $('body').append(X + '<br>')
    myFunction(123) // setter
    X = myFunction() // returns: 123
    $('body').append(X)

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

来源：https://stackoverflow.com/questions/15735821/setting-a-variable-in-the-closure-scope