| 72 | } |
| 73 | |
| 74 | function canUsePostMessage() { |
| 75 | // The test against `importScripts` prevents this implementation from being installed inside a web worker, |
| 76 | // where `global.postMessage` means something completely different and can't be used for this purpose. |
| 77 | |
| 78 | if (!global.postMessage || global.importScripts) { |
| 79 | return false; |
| 80 | } |
| 81 | |
| 82 | var postMessageIsAsynchronous = true; |
| 83 | var oldOnMessage = global.onmessage; |
| 84 | global.onmessage = function () { |
| 85 | postMessageIsAsynchronous = false; |
| 86 | }; |
| 87 | global.postMessage("", "*"); |
| 88 | global.onmessage = oldOnMessage; |
| 89 | |
| 90 | return postMessageIsAsynchronous; |
| 91 | } |
| 92 | |
| 93 | function canUseReadyStateChange() { |
| 94 | return "document" in global && "onreadystatechange" in global.document.createElement("script"); |