adding meta tags to head with javascript

gistfile1.js

var meta=document.createElement('meta');
meta.name='viewport';

meta.setAttribute('content', 'width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0');

document.getElementsByTagName('head')[0].appendChild(meta);

Although it is expected that the page is first rendered and only then it is crawled, I faced the same issue.
I wanted the search engines to respect the noindex tag, and tried an experiment of adding the tag in the body. That worked for me. I did this on zendesk in the article page hbs file. You can try adding the tag in the body if that is a possibility.
Moreover, the experiment took well over two weeks to show the effect.

@ayushxx7 Were you trying to load the meta tags through a script. I've tried adding it in the body too. But didn't work out.
Basically what I'm doing is keeping a script file with below content to be executed, So that all the meta tags will be appended in HEAD tag.

`
function createMetaTags(tags, type) {
var comment = document.createComment(type);
document.getElementsByTagName('head')[0].appendChild(comment);
tags.forEach(element => {
var attribute = Object.keys(element)[0];
var link = document.createElement('meta');
link.setAttribute(attribute, element[attribute]);
var metaKey = element[attribute].split(':');
var content = metaKey.length > 1 ? metaValues[metaKey[1]] : metaValues[metaKey[0]]
link.content = content;
document.getElementsByTagName('head')[0].appendChild(link);
});
}
var logoUrl = 'https://test/logo.svg';
var author = 'test';
var metaValues = {
title: "test.",
description: "test",
url: "test",
image: logoUrl,
'image:src': logoUrl,
type: "Website",
creator: author,
author: author,
site: author
}

var ogMeta = [
{ property: 'og:title' },
{ property: 'og:type' },
{ property: 'og:url' },
{ property: 'og:image' },
{ property: 'og:description' }
]

var twitterMeta = [
{ name: 'twitter:title' },
{ name: 'twitter:type' },
{ name: 'twitter:url' },
{ name: 'twitter:image' },
{ name: 'twitter:description' },
{ name: 'twitter:creator' },
{ name: 'twitter:image:src' }
]
var schemaMeta = [
{ itemprop: 'title' },
{ itemprop: 'type' },
{ itemprop: 'url' },
{ itemprop: 'image' },
{ itemprop: 'description' }
]

var meta = [
{ name: 'title' },
{ name: 'author' },
{ name: 'description' }
]

createMetaTags(meta, 'Primary Meta Tags')
createMetaTags(ogMeta, 'Open Graph / Facebook')
createMetaTags(twitterMeta, 'Twitter')
createMetaTags(schemaMeta, 'Schema.org markup for Google+')
`

I had the option to add the tag using article_page.hbs file. This file runs on every article in my Zendesk Help Center.
All I had to do was add the following to the beginning of that file:

{{#each article.labels}}
{{#is identifier 'noindex'}}<meta name="robots" content="noindex">{{/is}}
{{/each}}