Displays the exact wear 'float value' of CS:GO items in Steam inventories.

Steam_Inventory_Float_Value_Displayer.user.js

// ==UserScript==
// @name        Steam Inventory Float Value Displayer
// @description Displays the exact wear 'float value' of CS:GO items in Steam inventories.
// @namespace   zerf
// @include     http://steamcommunity.com/id/*/inventory*
// @include     http://steamcommunity.com/profiles/*/inventory*
// @include     https://steamcommunity.com/id/*/inventory*
// @include     https://steamcommunity.com/profiles/*/inventory*
// @version     1.1
// @grant       GM_xmlhttpRequest
// @grant       GM_getValue
// @grant       GM_setValue
// ==/UserScript==

let apikey = GM_getValue("steam_apikey");
let apiurl = "http://api.steampowered.com/IEconItems_730/GetPlayerItems/v0001";

let debug = false;

let log = (...msgs) => { console.log("[SIFV]", ...msgs); };
let dlog = (...msgs) => { if (debug) { log(...msgs); } }

let floatValueData = {};

// oddly enough, we don't have float_value data on anything
// in g_ActiveInventory, so we have to make an API call
let performAPICall = function() {
	// g_ActiveUser is null in the first tick...
	setTimeout(() => {
		let currentSteamId = unsafeWindow.g_ActiveUser.strSteamId;

		GM_xmlhttpRequest({
			method: "GET",
			url: `${apiurl}/?key=${apikey}&SteamID=${currentSteamId}`,
			onload: function(response) {
				let data = JSON.parse(response.responseText);

				if (!(data && data.result && data.result.items)) {
					log("Bad JSON received from Steam API!");
				}

				dlog(`Received ${data.result.items.length} items from the API`);

				for (let item of data.result.items) {
					if (!item.attributes) {
						dlog(`Item ${item.id} has no attributes.`);
						continue;
					}

					let wearAttribute = item.attributes.find((attr) => {
						return attr.defindex == 8;
					});

					if (!wearAttribute) {
						dlog(`Could not find wear attribute for item ${item.id}.`);
						continue;
					}

					floatValueData[item.id] = wearAttribute.float_value;
				}

				dlog("Successfully fetched API float value data.");
			}
		});
	}, 0);
}

let activeItemChanged = function(infoElement) {
	let selectedItem = unsafeWindow.g_ActiveInventory.selectedItem;

	if (!(selectedItem)) {
		log("No active item!");
		return;
	}

	dlog("Active item changed", selectedItem.id);

	let wearValue = floatValueData[selectedItem.id];

	if (wearValue == null) {
		dlog("Active item float value data has not been loaded!");
		return;
	}

	let floatValuePercent = ((1 - wearValue) * 100).toFixed(3);

	// add float value element to inventory panel
	let descriptors = infoElement.querySelector(".item_desc_descriptors");

	if (!descriptors) {
		log("Failed to grab item descriptor container element!");
		return;
	}

	let exteriorDescriptor = Array.from(descriptors.children).find((item) => {
		return item.innerText.indexOf("Exterior: ") !== -1;
	});

	if (exteriorDescriptor) {
		let floatValueElement = document.createElement("span");
		floatValueElement.innerText = ` (${floatValuePercent}%)`;
		exteriorDescriptor.appendChild(floatValueElement);
	} else {
		exteriorDescriptor = document.createElement("div");
		exteriorDescriptor.classList.add("descriptor");
		descriptors.insertBefore(exteriorDescriptor, descriptors.firstChild);

		let floatValueElement = document.createElement("span");
		floatValueElement.innerText = `Exterior: ${floatValuePercent}%`;
		exteriorDescriptor.appendChild(floatValueElement);
	}

	dlog("Appended float value element.");
}

let setupObserver = function() {
	let inventoryRight = document.querySelector(".inventory_page_right");

	if (!inventoryRight) {
		log("Failed to grab inventory right page element!");
		return;
	}

	let observer = new MutationObserver((mutations) => {
		mutations.forEach((mutation) => {
			if (mutation.type != "childList") { return; }
			if (!mutation.target.classList.contains("hover_item_name")) { return; }

			// a descendant has been added to the right page
			activeItemChanged(mutation.target.parentElement.parentElement);
		});
	});

	observer.observe(inventoryRight, { childList: true, subtree: true });
}

let promptForAPIKey = function() {
	let prompt_text = "Please enter your Steam web API key. "
	+ "This can be generated at https://steamcommunity.com/dev/apikey";

	let apikey = prompt(prompt_text);

	if (apikey) {
		GM_setValue("steam_apikey", apikey);
		location.reload();
	}
}

if (apikey) {
	performAPICall();
	setupObserver();

	log("Loaded.");
} else {
	log("User has no API key!");

	promptForAPIKey();
}

Hello. Can you show me, please, how use script on steam market CSGO? Im finded one script on github - but i dont know where i should take this info - || -s -i [ -g ] .
P.s. Thnx for your help.