Es6 函数式编程 MayBe函子的简单示例

var MayBe = function (val) {
    this.value = val;
}

MayBe.of = function (val) {
    return new MayBe(val);
}

MayBe.prototype.isNothing = function () {
    return (this.value === null || this.value === undefined);
}

MayBe.prototype.map = function (fn) {
    return this.isNothing() ? MayBe.of(null) : MayBe.of(fn(this.value));
}

// demo1： MayBe?{value: "Mr. GOOGLE"}
MayBe.of(‘Google‘)
     .map(_ => _.toUpperCase())
     .map(_ => "Mr. " + _)

// demo2： MayBe?{value: null}
MayBe.of(‘Google‘)
     .map(_ => undefined)
     .map(_ => "Mr. " + _)