这两个功能之间的区别 [英] Difference between these two functions

问题描述

在阅读"Javascript the Good Parts"时，在模块"一章中遇到了这段代码.

While reading "Javascript the Good Parts", came across this bit of code in the "module" chapter.

var serial_maker = function (  ) {

            // Produce an object that produces unique strings. A
            // unique string is made up of two parts: a prefix
            // and a sequence number. The object comes with
            // methods for setting the prefix and sequence
            // number, and a gensym method that produces unique
            // strings.

                var prefix = '';
                var seq = 0;

                return {
                    set_prefix: function (p) {
                        prefix = String(p);
                    },
                    set_seq: function (s) {
                        seq = s;
                    },
                    gensym: function ( ) {
                        var result = prefix + seq;
                        console.log(result);

                        seq += 1;
                        return result;
                    }
                };
            };
var seqer = serial_maker( );
seqer.set_prefix('Q');
seqer.set_seq(1000);
var unique = seqer.gensym( ); // unique is "Q1000

我的问题是:以上内容与此处的区别是什么?

My question is: whats the difference between the above and this bit here:

var other_serial_maker = function(pre, num){

        return pre + num;

    };

    var makeSerial = other_serial_maker("Q", 1000);

推荐答案

如果仅打算生成字符串 Q1000 ，则没有区别，但这不是重点.本书中的示例使用闭包，因此 prefix 和 seq 部分是私有的，只能从函数内部访问.

If you only objective to to generate the string Q1000 then no difference, but that's not the point. The example from the book is using a closure so that the prefix and seq parts are private and only accessible from within the function.

因此，您可以执行以下操作:

So the idea is, you can do this:

 var unique = seqer.gensym( ); // unique is "Q1000"

然后您可以执行此操作

 var anotherUnique = seqer.gensym( ); // unique is "Q1001"

因为 serial_maker 会跟踪其自身的状态，而您的代码不会.如果我们使用本书中的代码，则在设置 serial_maker 之后，我们可以根据需要多次调用 .gensym ，并获得不同的结果.使用您的代码，您需要以某种方式跟踪已经使用过的代码.

Because the serial_maker keeps track of it's own state, which your code does not. If we use the code from the book, then after setting up the serial_maker we could call .gensym as many times as we wanted and get a different result. With your code, you'd need to somehow keep track of which codes you've used already.

这篇关于这两个功能之间的区别的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！