Es6 函数式编程 MayBe函子的简单示例

Posted 2020-12-04 cylee

初级函子的作用非常简单，使用场景主要体现在：深入访问object的属性的时候，不会担心由于属性不存在、undefined、null等问题出现异常。

 

MayBe.js

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. " + _)