当我将一个 IIFE 的 typeof 记录到控制台时，它是一个对象而不是一个函数，为什么？

Question

I have an IIFE that returns an object. In my app.js file, which I add to a script tag in index.html, I log to the console typeof my IIFE and it is an object. Shouldn't it be a function? Why is typeof returning an object?

Here is my IIFE in app.js:

var UIController = (function() {

  var DOMstrings = {
    inputType: '.add__type',
    description: '.add__description',
    value: '.add__value',
    addBtn: '.add__btn'
  };

  return {
    getInput: function() {
      // return an object containing all values from UI elements
      return {
        type: document.querySelector(DOMstrings.inputType).value, // will be either income or expense
        description: document.querySelector(DOMstrings.description).value, // description of transaction
        value: document.querySelector(DOMstrings.value).value // value of transaction
      };
    },
    getDOMStrings: function() {
      return DOMstrings;
    }
  };

})();

console.log(typeof UIController);

Answer 1

IIFE stands for “immediately invoked function expression.” In other words, an expression created by invoking a function . Invoking a function means to call the function and produce a result. The value of an IIFE is the result of calling (invoking) the function, not the function itself.

In your example, the variable UIController is assigned the result of calling a function. Your function returned an object with two properties. The object is assigned to UIController . So typeof UIController produces object as expected.

Answer 2

**REMEMBER Immediately Invoked FUNCTION EXPRESSION FUNCTION (IIFE) are functions whose variables cannot be accessed outside the function & you cannot call that function explicitly(this will give error) **

*here is a simple code to clear concept of IIFE. this function just prints hey & do not have any return value *

var run=(function(){
  console.log("HEY");
  
})();
run(); //error
console.log(run);  HEY
console.log(typeof(run));  undefined

*Below IIFE functions returns the value *

var run=(function(){
 return 1;
  
})();
run(); //error
console.log(run);  5
console.log(typeof(run));  number