addIndex.js•1.67 kB
var _concat = require('./internal/_concat');
var _curry1 = require('./internal/_curry1');
var _slice = require('./internal/_slice');
var curryN = require('./curryN');
/**
* Creates a new list iteration function from an existing one by adding two new
* parameters to its callback function: the current index, and the entire list.
*
* This would turn, for instance, Ramda's simple `map` function into one that
* more closely resembles `Array.prototype.map`. Note that this will only work
* for functions in which the iteration callback function is the first
* parameter, and where the list is the last parameter. (This latter might be
* unimportant if the list parameter is not used.)
*
* @func
* @memberOf R
* @since v0.15.0
* @category Function
* @category List
* @sig ((a ... -> b) ... -> [a] -> *) -> (a ..., Int, [a] -> b) ... -> [a] -> *)
* @param {Function} fn A list iteration function that does not pass index or list to its callback
* @return {Function} An altered list iteration function that passes (item, index, list) to its callback
* @example
*
* var mapIndexed = R.addIndex(R.map);
* mapIndexed((val, idx) => idx + '-' + val, ['f', 'o', 'o', 'b', 'a', 'r']);
* //=> ['0-f', '1-o', '2-o', '3-b', '4-a', '5-r']
*/
module.exports = _curry1(function addIndex(fn) {
return curryN(fn.length, function() {
var idx = 0;
var origFn = arguments[0];
var list = arguments[arguments.length - 1];
var args = _slice(arguments);
args[0] = function() {
var result = origFn.apply(this, _concat(arguments, [idx, list]));
idx += 1;
return result;
};
return fn.apply(this, args);
});
});