javascript獲取當前HTML的header信息

function getHeaders(){
    var req = new XMLHttpRequest();
    req.open('GET', document.location.href, false);
    req.send(null);
    var headerArr = req.getAllResponseHeaders().split('\n');
    var headers = {};
    headerArr.forEach(item=>{
        if(item!==''){
		    var index = item.indexOf(':');
	        var key = item.slice(0,index);
	        var value = item.slice(index+1).trim();
	        headers[key] = value
	    }
	    
    })
    return headers
}

獲取單個header，例如：

xhr.getResponseHeader('date');
xhr.getResponseHeader('server');
xhr.getResponseHeader('transfer-Encoding');
xhr.getResponseHeader('content-type')