这个代码适用于我

<meta name="text" property="text" content="This is text" />
<meta name="video" property="text" content="http://video.com/video33353.mp4" />

JS

var x = document.getElementsByTagName("META");
    var txt = "";
    var i;
    for (i = 0; i < x.length; i++) {
        if (x[i].name=="video")
        {
             alert(x[i].content);
         }

    }    

示例:http://jsfiddle.net/muthupandiant/ogfLwdwt/

使用元根，然后获取和设置它的任何属性:

let meta = document.getElementsByTagName('meta')

console.log(meta.video.content)
> "http://video.com/video33353.mp4"

meta.video.content = "https://www.example.com/newlink"

function getDescription() {
    var info = document.getElementsByTagName('meta');
    return [].filter.call(info, function (val) {
        if(val.name === 'description') return val;
    })[0].content;
}

版本更新:

function getDesc() {
    var desc = document.head.querySelector('meta[name=description]');
    return desc ? desc.content : undefined;
}

你可以用这个:

function getMeta(metaName) {
  const metas = document.getElementsByTagName('meta');

  for (let i = 0; i < metas.length; i++) {
    if (metas[i].getAttribute('name') === metaName) {
      return metas[i].getAttribute('content');
    }
  }

  return '';
}

console.log(getMeta('video'));

下面是一个函数，它将返回任何元标记的内容并记住结果，避免不必要的DOM查询。

var getMetaContent = (function(){
        var metas = {};
        var metaGetter = function(metaName){
            var theMetaContent, wasDOMQueried = true;;
            if (metas[metaName]) {
                theMetaContent = metas[metaName];
                wasDOMQueried = false;
            }
            else {
                 Array.prototype.forEach.call(document.getElementsByTagName("meta"), function(el) {
                    if (el.name === metaName) theMetaContent = el.content;
                    metas[metaName] = theMetaContent;
                });
            }
            console.log("Q:wasDOMQueried? A:" + wasDOMQueried);
            return theMetaContent;
        }
        return metaGetter;
    })();

getMetaContent("description"); /* getMetaContent console.logs the content of the description metatag. If invoked a second time it confirms that the DOM  was only queried once */

下面是一个扩展版本，它也可以查询打开的图形标签，并使用array# some:

var getMetaContent = (function(){
        var metas = {};
        var metaGetter = function(metaName){
            wasDOMQueried = true;
            if (metas[metaName]) {
                wasDOMQueried = false;
            }
            else {
                 Array.prototype.some.call(document.getElementsByTagName("meta"), function(el) {
                        if(el.name === metaName){
                           metas[metaName] = el.content;
                           return true;
                        }
                        if(el.getAttribute("property") === metaName){
                           metas[metaName] = el.content;
                           return true;
                        }
                        else{
                          metas[metaName] = "meta tag not found";
                        }  
                    });
            }
            console.info("Q:wasDOMQueried? A:" + wasDOMQueried);
            console.info(metas);
            return metas[metaName];
        }
        return metaGetter;
    })();

getMetaContent("video"); // "http://video.com/video33353.mp4"

供参考，根据https://developer.mozilla.org/en-US/docs/Web/HTML/Element/meta全局属性是有效的，这意味着id属性可以与getElementById一起使用。