编辑代码

//JSRUN引擎2.0,支持多达30种语言在线运行,全仿真在线交互输入输出。 
function Num(init) {
    function Num2(init) {
        if (new.target !== null) {
            this.count = init
            this.add = (a) => {
                this.count = this.count + a
                return this
            }
            this.build = () => {
                return this.count
            }
        }
    }
    return new Num2(init)
}

console.log(Num(5).add(5).build())