this-curry

A simple and flexible way to curry functions, preserving this.

Install

Download the package through npm:

$ npm install this-curry

Or download it from the source.

Usage

// In the browser
<script src="/js/this-curry.min.js"></script>
// Use `window.curry`

// In Node
var curry = require('this-curry');

Syntax

curry(f, options)

• f: The function to curry.

• options: An options object that specifies the behaviour of the curried function. The available options are:

  • length: The expected length of the function. Usually determines how many arguments need to be passed before calling the function. Defaults to function.length.
  • latest_this: If true, use the context of the last call of the curried function when calling the given function, instead of saving the first. Defaults to false (Use the this that curry was called with).
  • name: Name of the curried function. Defaults to f.name.
  • validator: See customisations.

Examples

var sum = curry(function sum(a, b, c) {
  return a + b + c;
});

sum(1, 2, 3);
sum(1, 2)(3);
sum(1)(2, 3);
sum()(1)()(2)()()(3);  // All 6


var body_event_listener = curry.call(document.body, EventTarget.prototype.addEventListener, {
  length: 3
});


var body_on_click = body_event_listener('click');
var body_on_keydown = body_event_listener('keydown');

body_on_click(function(e) {
    // ...
}, false);

Customisations

options.validator should be a function that is called every time the curried function is called.

It is called with 4 arguments, args, length, f, name.

• args is an Arguments object of the arguments that have been passed so far.
• required_length is the length of the function.
• f is the original (uncurried) function.
• name is the name of the function.

It is also called with the context (this) that would call f if it needs to be called right now.

options.validator should return either true, false or another object.

If it returns false, the curried function returns another curried function, possible with some more arguments filled in.

If it returns true, the curried function calls the original function with the arguments that were given.

If it returns an object, that object could have the following properties:

• this: The new value for the context to call the original function with. (Alternatively that for linters that complain about the reserved word this)
• args: The new value for the arguments to call the original function with. Useful to remove invalid arguments. Should be an Array.
• length: The new value for the number of arguments before the function should be called. Passed as the length parameter to the validator function.
• f: The new function to replace the original function. For example, to change which function is called based on an argument.
• is_valid: A boolean for whether or not the function should be called. It is called if true. Defaults to false.

The default validator is curry.default_validator, which is simply:

function default_validator(args, required_length) {
  return args.length >= required_length;
}

(Which just checks if the length of the arguments is not less than the required length)

Another validator given is curry.limit_args, which will not pass in extra arguments, by returning an object with args sliced to the required length.

function add(a, b) {
  return a + b;
}

function sum() {
  return Array.prototype.reduce.call(arguments, add, 0);
}

var sum_5_or_more = curry(sum, { length: 5 });
var sum_5 = curry(sum, { length: 5, validator: curry.limit_args });

sum_5_or_more(1)(2, 3, 4)(5, 6, 7);  // 28
sum_5        (1)(2, 3, 4)(5, 6, 7);  // 15, as 6 and 7 are ignored.