使用原生javascript实现jquery的$(function(){ })

等DOM元素加载完成以后执行的代码

function _$(fun) {
        if (typeof fun != "function") {
            throw new typeError('The argument passed in is not a function');
        } else {
            var doc = document;
            if (doc.addEventListener) {
                doc.addEventListener("DOMContentLoaded", fun, false);
            } else {
                doc.onreadystatechange = function () {
                    if (doc.readyState == 'loader' || doc.readyState == 'complete' || doc.readyState == 'interactive') {
                        fun();
                    }
                }
            }
        }
    }
    _$(function () {
        alert('纳尼');
    });


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