CODEWITHSUNDEEP
javascriptcurrying
daneillone
daneillone

Reputation: 95

Js currying with condition

im trying to understand this code for long time i know currying function but confused with this code please explain theory behind 

var currying = function(fn) {
  var args = [];
  return function() {
    if (!!arguments.length){
      [].push.apply(args, arguments);
      return arguments.callee;
    } else {
      // what is 'this' in apply method
      return fn.apply(this, args);
    }
  }
} 

// currying var or args
// please explain the code below
var find = function(arr, el){
  return arr.indexOf(el) !== -1;
}

var newFind = currying(find)([1,2,3]);
console.log( newFind(1)());
console.log( newFind(2)());

Upvotes: 0

Views: 264

Answers (1)

Chase Choi
Chase Choi

Reputation: 1012

To make it easier to explain, let's convert the last part of the code:

// newFind = currying(find)([1,2,3]);
// console.log(newFind(1)());
// above is the same with below
console.log( currying(find)([1,2,3])(1)());

currying takes a function find so fn in currying is find. As it return a function, it can be called as it's shown on the code currying(find)([1,2,3])

let's look at this part, currying(find)([1,2,3]). It executes the returned method of currying. It can access the arguments with keyword arguments that is the array of [1,2,3] on the code.

The argument is the array which means it has the length value. Then the arguments is pushed into args array and return its callee which means inner method of currying.

As it returns method again, it can be called again with next paramter (1) of currying(find)([1,2,3])(1)(). Again, it executes the inner method of currying with arguments: 1. Then it is not an array so, it calls fn.apply(this, args). this keyword in the code means nothing in this case. you can replace this to null or you can use fn(...args) instead. the code is for converting array of argumnts to each argument. e.g. [[1,2,3], 1] is converted to [1,2,3], 1 Then, finally it executes find function with parameter [1,2,3], 1. You should remember all this thing is from returned method of currying so, you must call it as a function. append () at the end to execute the function.

Upvotes: 2

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