CODEWITHSUNDEEP
javascriptfunctionecmascript-6
Matt Kuhns
Matt Kuhns

Reputation: 1368

Calling a constructor function with parameters

I have a function that I cannot modify and I need to call it, but I haven't seen something like this before. 

var myCategorize = function(z) {
    return function(q) {
      return 1;
    }
 }('window'.indexOf('w') > 0 || window || false);

I have stripped out some of the code in the function(q) portion, just to simplify.

I think I have a curried function, so I tried this:

let category = myCategorize(bookTitles[i])(categories);

but when I do this I get the following error:

Uncaught TypeError: myCategorize(...) is not a function

So maybe this is an anonymous constructor function, so I try something like this:

let category = function(){myCategorize(bookTitles[i])(categories)};
console.log(category.apply());

I get the same error. How do I call this function and get the return value of 1?

Upvotes: 0

Views: 61

Answers (2)

VLAZ
VLAZ

Reputation: 28959

myCategorize is not a curried function, it's an IIFE implementing the module pattern. The brackets at the very end of the last line execute the top-level function(z):

var myCategorize = function(z) {
    return function(q) {
      return 1;
    }
 }('window'.indexOf('w') > 0 || window || false);
//^--------------------------------------------^

and pass in the value of z. It's clearer if I re-write it to add extra brackets and names bit:

var myCategorize = (function outer(z) {
//start of outer --^
    return function inner(q) {
      return 1;
    }
 })('window'.indexOf('w') > 0 || window || false);
//^-- end of outer

So what you have assigned to myCategorize is just inner. To execute it, simply add the brackets and a parameter:

var myCategorize = function(z) {
    return function(q) {
      return 1;
    }
 }('window'.indexOf('w') > 0 || window || false);

console.log("myCategorize", myCategorize);
var executionResult = myCategorize("foo");
console.log("executionResult", executionResult);

Upvotes: 2

Taki
Taki

Reputation: 17654

It's already calling the function once when adding the parenthesis, so the value of myCategorize is :

ƒ (q) {
  return 1;
}

Then you call that function with let category = myCategorize(bookTitles[i]) and the value of category is : 1

so, then equivalent of let category = myCategorize(bookTitles[i])(categories); is

let category = 1(categories); which throws that error

var myCategorize = function(z) {
  return function(q) {
    return 1;
  }
}('window'.indexOf('w') > 0 || window || false);

let category = myCategorize('x'); // 1

console.log(category);

let category2 = myCategorize('x')('y'); // throws, equovalent to 1('y');

Upvotes: 1

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