takeWhile.js•1.33 kB
var _curry2 = require('./internal/_curry2');
var _dispatchable = require('./internal/_dispatchable');
var _slice = require('./internal/_slice');
var _xtakeWhile = require('./internal/_xtakeWhile');
/**
* Returns a new list containing the first `n` elements of a given list,
* passing each value to the supplied predicate function, and terminating when
* the predicate function returns `false`. Excludes the element that caused the
* predicate function to fail. The predicate function is passed one argument:
* *(value)*.
*
* Dispatches to the `takeWhile` method of the second argument, if present.
*
* Acts as a transducer if a transformer is given in list position.
*
* @func
* @memberOf R
* @since v0.1.0
* @category List
* @sig (a -> Boolean) -> [a] -> [a]
* @param {Function} fn The function called per iteration.
* @param {Array} list The collection to iterate over.
* @return {Array} A new array.
* @see R.dropWhile, R.transduce, R.addIndex
* @example
*
* var isNotFour = x => x !== 4;
*
* R.takeWhile(isNotFour, [1, 2, 3, 4, 3, 2, 1]); //=> [1, 2, 3]
*/
module.exports = _curry2(_dispatchable('takeWhile', _xtakeWhile, function takeWhile(fn, list) {
var idx = 0;
var len = list.length;
while (idx < len && fn(list[idx])) {
idx += 1;
}
return _slice(list, 0, idx);
}));