JS中的惰性函数

水深无声 2022-05-26 06:45 148阅读 0赞

最近在网上看一个关于惰性函数的例子，觉得非常不错，就记下来。

/** * Created by DreamCatcher on 2018/4/26. */
    function createXHR () { 
        var xhr = null;
        try {
            //Firefox, Opera8.0+, Safari, IE7+
            xhr = new XMLHttpRequest();
        } catch (e) {
            try {
                xhr = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    xhr = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {
                    xhr = null;
                }
            }
        }
        return xhr;
    }
    
    /* 惰性函数 */
    function createXHR () { 
        var xhr = null;
        if (XMLHttpRequest) {
            xhr = new XMLHttpRequest();
            createXHR = function () { 
                return new XMLHttpRequest();
            }
        } else {
            try {
                xhr = new ActiveXObject("Msxml2.XMLHTTP");
                createXHR = function () { 
                    return new ActiveXObject("Msxml2.XMLHTTP");
                }
            } catch (e) {
                try {
                    xhr = new ActiveXObject("Microsoft.XMLHTTP");
                    createXHR = function () { 
                        return new ActiveXObject("Microsoft.XMLHTTP");
                    }
                } catch (e) {
                    xhr = null;
                    createXHR = function () { 
                        return null;
                    }
                }
            }
        }
        return xhr;
    }

以下是第二种实现方式：