steam-clear-wishlist.js

(
function() {
	let div = '<div id="progress" style="position: fixed; z-index: 1000; background-color: #424c59; padding: 1em; bottom: 1em; left: 1em; border-radius: 4px; box-shadow: 1px 2px 12px 0 black">Clearing wishlist...</div>';
	document.querySelector("body").innerHTML+=div;
	let progress = document.getElementById("progress");

	let promises = [], count = 0;
	for (let id of g_Wishlist.rgAllApps) {
		let form = new FormData(); 
		form.append('sessionid', g_sessionID); 
		form.append('appid', id);
		
		promises.push(fetch(g_strWishlistBaseURL+'remove', {method: 'POST', body: form}).then(() => {
			let msg = "removed app "+id+", total removed: "+count;
			console.log(msg);
			progress.innerHTML=msg;
			count++;
		}));
	}

	Promise.all(promises).then(() => {
		console.log("done removing. refreshing...");
		progress.parentNode.removeChild(progress);
		location.reload();
	});
}
)();

Thank you for this. I tried it, and it hit a rate-limit, but it's certainly a useful start.

For anyone else that stumbles upon this, there's a serial version of roughly the same idea at https://www.reddit.com/r/Steam/comments/ah9as8/comment/eecsutc/. It seems to get through about 4 per second right now, so if you can wait, or your wishlist is small, that might be simple-enough.