Invocation And Performance Navigation — Part 1 MCQs with Explanations

The property performance.memory gives access to the JavaScript memory usage data.

Each performance.timing attribute shows the time of a navigation event (such as when the page was requested) or page load event (such as when the DOM began loading), measured in milliseconds.

The properties associated with the Response event are : 1. responseStart 2. responseEnd.

The time taken for page load once the page is received from the server: loadEventEnd-responseEnd .

The following properties are associated with the Processing event : 1. domComplete 2. domContentLoaded 3. domInteractive 4. domLoading 5. unLoadEnd

When the type attribute of the navigation object is set to 2, it means that the navigation is done by moving back or forward through history.

The Performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds, accurate to one thousandth of a millisecond equal to the number of milliseconds since the PerformanceTiming.navigationStart property and the call to the method.

Both PerformanceTiming.navigationStart and also the PerformanceTiming.fetchStart are a read-only properties.

PerformanceTiming is an interface in JavaScript.

There are a total of 2 properties associated with the Response event namely : 1. PerformanceTiming.responseEnd 2. PerformanceTiming.responseStart

There are a total of 7 properties in the prototype object namely : 1. perceivedTime 2. redirectTime 3. cacheTime 4. dnsLookupTime 5. tcpConnectionTime 6. roundTripTime 7. pageRenderTime

JSON.stringify does not serialize undefined values or functions within an object.

There are a total of 23 properties associated with the interface PerformanceTiming.

There are totally 2 properties associated with the window.performance and they are: 1. navigation 2. type

The navigation tells how the user navigated to the page.

The PerformanceTiming.navigationStart read-only property returns an unsigned long long representing the moment, in miliseconds since the UNIX epoch, right after the prompt for unload terminates on the previous document in the same browsing context. If there is no previous document, this value will be the same as : PerformanceTiming.fetchStart.

JSON.stringify does not serialize undefined values or functions within an object.

The PerformanceTiming.fetchStart read-only property returns an unsigned long long representing the moment, in miliseconds since the UNIX epoch, the browser is ready to fetch the document using an HTTP request.

The Request event has only one property : requestStart.

The timing code is in the page, so it affects how the page loads and the time that takes.. The Navigation Timing API can be used to get the timing without affecting the page loading process.

There are a total of 2 read-only attributes present in the navigator object namely : 1. redirectCount 2. type

HTTP redirects are significant because they cause a complete roundtrip for each redirect. The original request is returned from the web server as either a 301 or a 302 with the path to the new location. The browser must then initialize a new TCP connection and send a new request for the new location.

The DNS reply goes to the Browser in a single HTTP redirect.

The redirectCount property can be accessed as : performance.navigation.redirectCount.

Totally 4 constant values can be represented by the property type.

TYPE_RESERVED: Has the value of 255 and is a catch-all for any navigation type not defined above.

TYPE_RELOAD: Has the value of 1, indicating that the current page was arrived at via a reload operation.

TYPE_BACK_FORWARD: Has the value of 2, indicating that the page was navigated to via the browser history, either using the back or forward buttons or programmatically through the browser’s history object.

TYPE_BACK_FORWARD: Has the value of 2, indicating that the page was navigated to via the browser history, either using the back or forward buttons or programmatically through the browser’s history object.

The DNS Lookup directs to the DNS Server.

There are a total of 3 memory objects namely : 1. jsHeapSizeLimit 2. totalJsHeapSize 3. usedJsHeapSize

The heap is the collection of JavaScript objects that the interpreter keeps in resident memory.

The memory object is a feature of Chrome that allows us to see the memory usage that Chrome is taking up while running our page.

The command performance.memory. jsHeapSizeLimit is used to access the Heap size limit.

When the interpreter sees an object in the heap with no object references, it removes that object from the heap. This is called garbage collection.

The usedJsHeapSize property is the amount of memory that all of the current objects in the heap are using.

The totalJsHeapSize is size of the heap including free space not used by objects.

Profiling allows us to monitor our memory usage.

Typing about:memory into the location bar brings up a page that gives a high-level breakdown of memory usage.

To get a more granular insight of the memory usage, we must type about:memory?verbose.