javascript - Two sets of parentheses after function call - Stack Overflow

admin管理员组

文章数量:1134247

I was looking how filters works in Angularjs and I saw that we need to send 2 sets of parentheses.

$filter('number')(number[, fractionSize])

What does it means and how do we handle it with JavaScript?

I was looking how filters works in Angularjs and I saw that we need to send 2 sets of parentheses.

$filter('number')(number[, fractionSize])

What does it means and how do we handle it with JavaScript?

• javascript
• angularjs

Share Improve this question Follow edited Aug 14, 2013 at 14:32 M Abbas 6,47944 gold badges3535 silver badges4848 bronze badges asked Aug 14, 2013 at 14:28 L105L105 5,41933 gold badges1919 silver badges2323 bronze badges 3

• 8 Personally I find this syntax confusing / awkward to read as well. But you can use simpler syntax to access AngularJS filters as described here: stackoverflow.com/a/14303362/1418796 – pkozlowski.opensource Commented Aug 14, 2013 at 14:41
• I took angularjs as an exemple. I wanted to know how to handle this if I create a function myself. – L105 Commented Aug 14, 2013 at 14:45
• 7 Actually it's called "currying". a programming technique. – Sajuuk Commented Jul 26, 2018 at 11:52

Add a comment  | 

4 Answers 4

Sorted by: Reset to default 404

It means that the first function ($filter) returns another function and then that returned function is called immediately. For Example:

function add(x){
  return function(y){
    return x + y;
  };
}

var addTwo = add(2);

addTwo(4) === 6; // true
add(3)(4) === 7; // true

$filter('number') returns a function that accepts two arguments, the first being required (a number) and the second one being optional (the fraction size).

It's possible to immediately call the returned function:

$filter('number')('123')

Alternatively, you may keep the returned function for future use:

var numberFilter = $filter('number');

numberFilter('123')

It is the same as this:

var func = $filter('number');
func(number[, fractionSize]);

The $filter() function returns a pointer to another function.

with ES6 or later versions you can do it that way;

const divideBoth = (x) => (y) => {
   return x / y;
};

one of the reasons that makes this function type useful is when you have a react.js component that needs have callback function instead of doing it inline way(which is ()=>return value) you can do it the way we did previously. But it is not recommended to use in event callbacks because it gets execute in the first render which might cause issues sometimes

本文标签： javascriptTwo sets of parentheses after function callStack Overflow