JavaScript named predicate helper (Symbol#to_proc from Ruby)

to-function.js

"use strict";
// Make predicate funtions more convenient.
// Works like Ruby's Symbol#to_proc, which is usually called with the unary & operator and a Symbol literal:
//   (ruby) %w[one two three].map(&:upcase)   # returns ["ONE", "TWO", "THREE"]
//   (js)   ['one', 'two', 'three'].map(toFn('toUpperCase'));  // returns ["ONE", "TWO", "THREE"]
//   (js)   ['one', 'two', 'three'].map(toFn`toUpperCase`);    // same as above, but called via tagged string literal
// @param name {String} Name of method
// @param ...bound_args Arguments to bind NOTE: Args cannot be bound when calling as a tagged-template
// @return {Function} Function to call named method with bound args on any object given at time of invocation
module.exports = function toFn( name, ...bound_args ){
  if( name instanceof Array ){
    if( name.length > 1 || bound_args.length > 0 ) throw 'Tagged-template calls must not contain expressions';
    name = name[0];
  }

  return (obj, ...args) => obj[name](...bound_args, ...args);
};