A bookmarklet to save current page's code/form, like a textarea cache (except it doesn't save automatically).

store(code); bookmarklet.js

javascript:(()=>{
	let magic="store(code);",hn=location.hostname,d=document,qS=(s,o=document)=>o.querySelector(s),
	element,value,description=[new Date().getTime()];
	if(/openprocessing\.org/.test(hn)){
		element=codeMirror;
		value=element.getValue();
	}else if(/(wavepot|tinyrave)\.com/.test(hn)){
		element=ace.edit("editor").getSession();
		value=element.getValue();
	}else if(/mytextarea\.com/.test(hn)){
		element=d.getElementById("textarea");
		value=element.value;
	}else if(/editpad\.org/.test(hn)){
		/*This site isn't made to preserve your text.*/
		element=d.textform.text;
		value=element.value;
	}else if(/glslsandbox\.com/.test(hn)){
		/*TODO: Fix this.*/
		element=d.getElementsByClassName("CodeMirror-lines")[0];
		value=element.innerText;
	}else if(/shadertoy\.com/.test(hn)){
		/*TODO: Fix this.*/
		element=d.getElementsByClassName("CodeMirror-code")[0];
		value=Array.from(element.getElementsByTagName("pre")).map(x=>x.innerText).join("");
	}else if(/pastebin\.com/.test(hn)){
		element=d.getElementById("paste_code");
		value=element.value;
	}else if(/codeshare\.io|(gist\.github|jshint)\.com/.test(hn)){
		element=qS(".CodeMirror").CodeMirror;
		value=element.getValue();
	}else if(/collabedit\.com/.test(hn)){
		element=qS("textarea");
		value=element.value;
	}else if(/wik(tionary|ipedia).org/.test(hn)){
		let p=new URL(location).searchParams;
		element=qS("div[class='wikiEditor-ui-text']").firstChild;
		value=element.value;
		description.push(p.get("title"));
	}else if(/4chan(nel)?.org/.test(hn)){
		/*TODO: 8ch.net (dead), lainchan.org, thread ID.*/
		let header=qS("tr[data-type='Comment'] textarea"),
		    floating=qS("div[id='qrForm'] textarea[name^='com']");
		if(header!==null){element=header;value=element.value;description.push("header comment");}
		if(floating!==null){element=floating;value=element.value;description.push("floating comment");}
	}else{
		console.error("Unknown domain name.");
	}
	let stored=Object.keys(localStorage).filter(x=>x.startsWith(magic)),
	    save=()=>{
		if(value.length){
			console.log(value);
		}else if(confirm("The string is empty. Would you like to cancel?")){
			return;
		}
		let i=stored.findIndex(x=>value===localStorage.getItem(x));
		if(i>=0){
			alert(`An identical already exists “${stored[i]}”.`);
		}else{
			let k=`${magic} (${description.join(", ")})`;
			localStorage.setItem(k,value);
			alert(`Saved as “${k}”.`);
		}
	};
	if(stored.length&&confirm("Read older storage?\n(Otherwise save.)")){
		if(value!==undefined&&confirm("Save current one beforehand?")){
			save();
		}
		if(confirm(`Go through?\n${stored.length}: ${stored.join(", ")}`)){
			for(let i=0;i<stored.length;i++){
				if(confirm(`Load this?\n${stored[i]}\n${localStorage.getItem(stored[i])}`)){
					element.value=localStorage.getItem(stored[i]); /*TODO*/
					break;
				}
			}
		}
	}else if(value!==undefined){
		save();
	}else{
		alert("There's nothing.");
	}
})();

To read (on mobile):

javascript:(()=>{
	let k=Object.keys(localStorage).filter(x=>x.startsWith("store(code);"));
	if(confirm(k.length+": "+k.join(","))){
		k.forEach(x=>prompt(x,localStorage.getItem(x)));
	}
})();

To remove:

javascript:(()=>{
	let k=Object.keys(localStorage).filter(x=>x.startsWith("store(code);"));
	if(confirm(k.length+" to remove: "+k.join(","))){
		k.forEach(x=>{
			if(confirm("Remove?\n"+localStorage.getItem(x))){
				localStorage.removeItem(x);
			}
		});
	}
})();

• I should add a function to restore from storage.

Now it looks kinda bad.

• I think I'd also like to read their dates, to see when they were saved as in “x hours ago”, “x days ago”.

{let magic="store(code); ";Object.keys(localStorage).filter(x=>x.startsWith(magic)).map(x=>new Date(+x.substring(magic.length).match(/\d+/)[0]));}

• Could be helpful to add an ability to remove old items from within the script.
• It shouldn't ask to restore if there aren't any stored, which would make it more explanatory as well not to start with this question to someone first time using it.
• Avoid storing an identical value.
• Ask to replace the previous one? (I'm not sure if it's good or not.)
• Add Google, Discord, Repl.it, p5.js editor, online text editor tools.
• On OpenProcessing, inside the div.codeContainer there's div#codeTabs above div[class^="CodeMirror"], and li.selected within the ul element is the current tab.