Function becomes undefined when declaring local variable with same name

Question

I have declared a function in file so that it becomes global:

相关标签:

Answer 1

It's because of javascript's hoisting

function() {
        var speakService = speakService();
        return speakService;
    }

Will be same as

function() {
        var speakService; //Declaration moved to top
        speakService = speakService(); //here speakService is undefined
        return speakService;
    }

Answer 2

The reason why the variable appears to be undefined is hoisting. When you write something like var x = 3 the definition of x is hoisted to the top of the current scope (functional in this case since you are using var). The assignment itself happens when you hit that particular line.

So in your specific case, when you enter the scope of that variable you define it var speakService first, which hides the function speakService from the rest of the scope. Then you try to execute the line speakService = speakService() and since speakService is just an uninitialized variable you get undefined.

Answer 3

Like others have said, your issue is hoisting. Just return an object literal and use the IIFE pattern.

var myService = (function speakService() {
    var speak = function(word) {
        console.log(word);
    };
  
    return {
      speak: speak
    };
})();

myService.speak("TEST");