HMR

需要处理的兼容性问题

DOM

• document.createElement("script")
• document.head.appendChild(script)
• location
• iframe

/******/ 	function hotDownloadUpdateChunk(chunkId) {
/******/ 		var script = document.createElement("script");
/******/ 		script.charset = "utf-8";
/******/ 		script.src = __webpack_require__.p + "" + chunkId + "." + hotCurrentHash + ".hot-update.js";
/******/ 		if (null) script.crossOrigin = null;
/******/ 		document.head.appendChild(script);
/******/ 	}

XMLHttpRequest

• open
• timeout
• send
• onreadystatechange
• readystate
• status
• responseText

/******/ 	function hotDownloadManifest(requestTimeout) {
/******/ 		requestTimeout = requestTimeout || 10000;
/******/ 		return new Promise(function(resolve, reject) {
/******/ 			if (typeof XMLHttpRequest === "undefined") {
/******/ 				return reject(new Error("No browser support"));
/******/ 			}
/******/ 			try {
/******/ 				var request = new XMLHttpRequest();
/******/ 				var requestPath = __webpack_require__.p + "" + hotCurrentHash + ".hot-update.json";
/******/ 				request.open("GET", requestPath, true);
/******/ 				request.timeout = requestTimeout;
/******/ 				request.send(null);
/******/ 			} catch (err) {
/******/ 				return reject(err);
/******/ 			}
/******/ 			request.onreadystatechange = function() {
/******/ 				if (request.readyState !== 4) return;
/******/ 				if (request.status === 0) {
/******/ 					// timeout
/******/ 					reject(
/******/ 						new Error("Manifest request to " + requestPath + " timed out.")
/******/ 					);
/******/ 				} else if (request.status === 404) {
/******/ 					// no update available
/******/ 					resolve();
/******/ 				} else if (request.status !== 200 && request.status !== 304) {
/******/ 					// other failure
/******/ 					reject(new Error("Manifest request to " + requestPath + " failed."));
/******/ 				} else {
/******/ 					// success
/******/ 					try {
/******/ 						var update = JSON.parse(request.responseText);
/******/ 					} catch (e) {
/******/ 						reject(e);
/******/ 						return;
/******/ 					}
/******/ 					resolve(update);
/******/ 				}
/******/ 			};
/******/ 		});
/******/ 	}