How can I make a function visible in function expressions when it's currently not showing up?

Here's a function expression that I have:

var inputChecker = function(field) {
    return function() {
        if(field === '' || field === 'undefined' || field === null) {
            return false;
        }
        return true;
    }
}  

I intend to use this function in various other function expressions:

(function($) {
  if(inputChecker(x)) {}
})(jQuery);


(function($) {

})(jQuery);

However, the issue is that inputChecker is not accessible in these function expressions when it's defined outside of their bodies. Why is that so? Shouldn't inputChecker be considered global?

Answer №1

Dystroy's answer may be simpler, but if you prefer another approach...

The result of the inputChecker function is not a boolean, it is actually a function. To execute the returned function, utilize the () expression:

var func = inputChecker(x); // retrieves the function
func(); // executes the returned function

or simply

inputChecker(x)();

In your script

(function($) {
  if(inputChecker(x)()) {
    // insert your custom code here if x is defined
  }
})(jQuery);

Just a reminder: to check if a variable is not undefined, omit the quotation marks - undefined is a constant, not a string

if(field===undefined)

Answer №2

Your code snippet demonstrates the concept of a function factory, which creates a function that can check a specific property rather than returning a boolean directly.

While this approach can be handy, there are a couple of issues to consider:

  • Within the returned function, you are only checking a fixed value passed by the factory. Since this value remains constant (due to closure), the resulting function essentially boils down to a simplistic true/false determination, rendering it somewhat redundant.

  • Calling `inputChecker(x)` as if it functions like a boolean instead of a function may lead to confusion.

If your goal is straightforward property checking, a cleaner alternative could be:

var checkInput = function(field) {
    if(field === '' || field === 'undefined' || field === null){
        return false;
    }
    return true;
}  

However, if you desire to generate varying checking functions based on a different variable, you could employ the function factory pattern as illustrated below:

var x = true;
var checkInput = (function (x) {
    if (x === true) {
        return function(field) {
            if(field === '' || field === 'undefined' || field === null){
                return false;
            }
            return true;
        }
    } else {
       return function(field) {
           //handle field differently here
       }
    }
}(x));

With this setup, the assignment of a specific function to `checkInput` depends on the value of `x`.

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