js动态向 head 标签中引入js文件

function dynamicLoadJs(url, callback) {
    var head = document.getElementsByTagName('head')[0];
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = url;
    if (typeof (callback) == 'function') {
        script.onload = script.onreadystatechange = function () {
            if (!this.readyState || this.readyState === "loaded" || this.readyState === "complete") {
                callback();
                script.onload = script.onreadystatechange = null;
            }
        };
    }
    head.appendChild(script);
}

//引入的js文件地址
let url='https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.js'
dynamicLoadJs(url);