将变量从out函数传递给内部函数

Question

In an object literal, in a function definition, I invoke another function and pass it a function definition.

...

var myObjLiteral = {
    ...
    , check_on: function(param1, param2) {
           ref.otherFunction(param1, function(param2){checkJson(param2)}); 
    }
}

otherFunction will receive param1 as is, but it won't receive param2 as is.

Why?

Because the second parameter passed to other function creates it's own closure and param2 is actually a new reference which overrides the outer reference of param2 in definition of check_on.

I think this is correct. But more importantly, how do I pass the valur of param2 into the function definition I pass as the second parameters into otherFunction?

Thanks

Answer 1

Just remove the param2 param,(anotherParam is not necessary, just to illustrate the problem)

    otherFunction(param1, function(anotherParam) {

        checkJson(param2);
    });

so the function will become a closure for param2.

Lets assume otherFunction is like this:

 otherFunction = function(p1, callback){}

Then callback(123456) will make the anotherParam = 123456;

Answer 2

It's because when you declare param2 in the second function it creates a new variable with that name inside the second function. Thus closure is broken. Remove the declaration of param2 or rename it to let closure work.

This tutorial helped me understand better how closure works.

Answer 3

Below is how I've worked this out to help me illustrate Andrew's answer to myself. You might find this useful:

var myObjLiteral = {

  check_on: function (param1, param2) {
    var _this = this;
    this.otherFunction(param1, function () {
        _this.checkJson(param2);
    });
  },

  otherFunction:  function(param1, callback) {
    console.log('otherFunction', param1); // otherFunction 1
    callback();
  },

  checkJson: function (param2) {
    console.log('checkJson', param2); // checkJson 2
  }

}

myObjLiteral.check_on(1, 2);