Underscore.js 1.7の使い方 Functions編 negate

var r = document.getElementById("r");
var isFalse = _.negate(Boolean);
var isNotNumber = _.negate(Number);
r.innerHTML = _.find([-2, -1, 0, 1, 2], isFalse);
// => 0
r2.innerHTML = _.find([1, 2, 'three', 4], isNotNumber);
// => three