Edit in JSFiddle

function run() {
    var val1 = _.reduce([1, 2, 3], function (v, a) {
        return v + a;
    });

    val2 = _([1, 2, 3]).reduce(function (v, a) {
        return v + a;
    });
    console.log(val1 === val2);

    var eachVal = [1, 2, 3, 4];
    
    //Yeilds each element to function
    t = _(eachVal).each(function (v) {
        return v * v;
    });

    console.log(t === undefined);

    //Returns a new map of yielded elements
    t = _(eachVal).map(function (v) {
        return v * v;
    });

    console.log(t.toString() === [1, 4, 9, 16].toString());
}

<button type="button" onClick='run()'>Run</button>