链式操作的核心原理

test.js

var c = require('./chained1');
// c.select();
c.where('id=2').select();

chained.js

module.exports = {
    where: function (wh) {
        this.whe = wh;
        // 链式操作的核心就是保存数据并返回本对象
        return this;
    },
    select: function () {
        if (this.whe == undefined) {
            var sql = "select * from users ";
        } else {
            var sql = "select * from users where " + this.whe;
        }
        console.log(sql);
        this.whe = undefined;
    },
    update:function(){
        if (this.whe == undefined) {
            console.log('更新数据时，请填写where条件');
            return;
        } else {
            var sql = "update xx from  set () where " + this.whe;
        }
        console.log(sql);
        this.whe = undefined;
    }
}