spots

Partial function argument binding with placeholders

spots makes it simple to bind some arguments, leaving the rest free.

var S = require('spots');
function sub(a, b) {
  return a - b;
}
// use library itself as a placeholder
var minus1 = S(sub, S, 1);
// minus1 = sub(_, 1) function
minus1(9); // 8, same as sub(9, 1);

It can apply more than 1 argument.

function add4(a, b, c, d) { return a + b + c + d; }
var applyEven = S(add4, S, 1, S, 2);
applyEven(-1, -2); // 0
// equivalent to add4(-1, 1, -2, 2);

It works very nice to solve JavaScript Madness problem.

['1', '2', '3'].map(S(parseInt, S, 10));
// returns [1, 2, 3]

You can use spots with functional-pipeline to apply arguments to the individual steps.

var fp = require('functional-pipeline');
function add(a, b) { return a + b; }
function sub(a, b) { return a - b; }
fp(
  S(sub, 1, S),
  S(add, S, 20)
)(3); // 18
// same as
// add( sub(1, 3), 20 )

Real world example chdir-promise index.js where we use spots to pass argument to Q.try method.

If there is a context (like filling some arguments to a method), you can bind to the object after applying spots

var calc = {
  name: 'calc',
  add4: function (a, b, c, d) {
    return this.name + ' ' + a + b + c + d;
  }
};
var add_2_4 = S(calc.add4, S, 2, S, 4).bind(calc);
add_2_4(1, 3); // calc 10

Related:

• Point-free is not pointless
• Selective application
• functional-pipeline
• heroin

Available on NPM and bower under name spots.

Small print

Author: Gleb Bahmutov © 2014

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Spread the word: tweet, star on github, etc.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2014 Gleb Bahmutov

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.