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/******************************************************************************
Copyright (c) 2014, Google Inc.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
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may be used to endorse or promote products derived from this software
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******************************************************************************/
/******************************************************************************
*******************************************************************************
Calculates the Speed Index for a page by:
- Collecting a list of visible rectangles for elements that loaded
external resources (images, background images, fonts)
- Gets the time when the external resource for those elements loaded
through Resource Timing
- Calculates the likely time that the background painted
- Runs the various paint rectangles through the SpeedIndex calculation:
https://sites.google.com/a/webpagetest.org/docs/using-webpagetest/metrics/speed-index
TODO:
- Improve the start render estimate
- Handle overlapping rects (though maybe counting the area as multiple paints
will work out well)
- Detect elements with Custom fonts and the time that the respective font
loaded
- Better error handling for browsers that don't support resource timing
*******************************************************************************
******************************************************************************/
var RUMSpeedIndex = function(win) {
win = win || window;
var doc = win.document;
/****************************************************************************
Support Routines
****************************************************************************/
// Get the rect for the visible portion of the provided DOM element
var GetElementViewportRect = function(el) {
var intersect = false;
if (el.getBoundingClientRect) {
var elRect = el.getBoundingClientRect();
intersect = {'top': Math.max(elRect.top, 0),
'left': Math.max(elRect.left, 0),
'bottom': Math.min(elRect.bottom, (win.innerHeight || doc.documentElement.clientHeight)),
'right': Math.min(elRect.right, (win.innerWidth || doc.documentElement.clientWidth))};
if (intersect.bottom <= intersect.top ||
intersect.right <= intersect.left) {
intersect = false;
} else {
intersect.area = (intersect.bottom - intersect.top) * (intersect.right - intersect.left);
}
}
return intersect;
};
// Check a given element to see if it is visible
var CheckElement = function(el, url) {
if (url) {
var rect = GetElementViewportRect(el);
if (rect) {
rects.push({'url': url,
'area': rect.area,
'rect': rect});
}
}
};
// Get the visible rectangles for elements that we care about
var GetRects = function() {
// Walk all of the elements in the DOM (try to only do this once)
var elements = doc.getElementsByTagName('*');
var re = /url\(.*(http.*)\)/ig;
for (var i = 0; i < elements.length; i++) {
var el = elements[i];
var style = win.getComputedStyle(el);
// check for Images
if (el.tagName == 'IMG') {
CheckElement(el, el.currentSrc || el.src);
}
// Check for background images
if (style['background-image']) {
re.lastIndex = 0;
var matches = re.exec(style['background-image']);
if (matches && matches.length > 1)
CheckElement(el, matches[1].replace('"', ''));
}
// recursively walk any iFrames
if (el.tagName == 'IFRAME') {
try {
var rect = GetElementViewportRect(el);
if (rect) {
var tm = RUMSpeedIndex(el.contentWindow);
if (tm) {
rects.push({'tm': tm,
'area': rect.area,
'rect': rect});
}
}
} catch(e) {
}
}
}
};
// Get the time at which each external resource loaded
var GetRectTimings = function() {
var timings = {};
var requests = win.performance.getEntriesByType("resource");
for (var i = 0; i < requests.length; i++)
timings[requests[i].name] = requests[i].responseEnd;
for (var j = 0; j < rects.length; j++) {
if (!('tm' in rects[j]))
rects[j].tm = timings[rects[j].url] !== undefined ? timings[rects[j].url] : 0;
}
};
// Get the first paint time.
var GetFirstPaint = function() {
// Try the standardized paint timing api
try {
var entries = performance.getEntriesByType('paint');
for (var i = 0; i < entries.length; i++) {
if (entries[i]['name'] == 'first-paint') {
navStart = performance.getEntriesByType("navigation")[0].startTime;
firstPaint = entries[i].startTime - navStart;
break;
}
}
} catch(e) {
}
// If the browser supports a first paint event, just use what the browser reports
if (firstPaint === undefined && 'msFirstPaint' in win.performance.timing)
firstPaint = win.performance.timing.msFirstPaint - navStart;
if (firstPaint === undefined && 'chrome' in win && 'loadTimes' in win.chrome) {
var chromeTimes = win.chrome.loadTimes();
if ('firstPaintTime' in chromeTimes && chromeTimes.firstPaintTime > 0) {
var startTime = chromeTimes.startLoadTime;
if ('requestTime' in chromeTimes)
startTime = chromeTimes.requestTime;
if (chromeTimes.firstPaintTime >= startTime)
firstPaint = (chromeTimes.firstPaintTime - startTime) * 1000.0;
}
}
// For browsers that don't support first-paint or where we get insane values,
// use the time of the last non-async script or css from the head.
if (firstPaint === undefined || firstPaint < 0 || firstPaint > 120000) {
firstPaint = win.performance.timing.responseStart - navStart;
var headURLs = {};
var headElements = doc.getElementsByTagName('head')[0].children;
for (var i = 0; i < headElements.length; i++) {
var el = headElements[i];
if (el.tagName == 'SCRIPT' && el.src && !el.async)
headURLs[el.src] = true;
if (el.tagName == 'LINK' && el.rel == 'stylesheet' && el.href)
headURLs[el.href] = true;
}
var requests = win.performance.getEntriesByType("resource");
var doneCritical = false;
for (var j = 0; j < requests.length; j++) {
if (!doneCritical &&
headURLs[requests[j].name] &&
(requests[j].initiatorType == 'script' || requests[j].initiatorType == 'link')) {
var requestEnd = requests[j].responseEnd;
if (firstPaint === undefined || requestEnd > firstPaint)
firstPaint = requestEnd;
} else {
doneCritical = true;
}
}
}
firstPaint = Math.max(firstPaint, 0);
};
// Sort and group all of the paint rects by time and use them to
// calculate the visual progress
var CalculateVisualProgress = function() {
var paints = {'0':0};
var total = 0;
for (var i = 0; i < rects.length; i++) {
var tm = firstPaint;
if ('tm' in rects[i] && rects[i].tm > firstPaint)
tm = rects[i].tm;
if (paints[tm] === undefined)
paints[tm] = 0;
paints[tm] += rects[i].area;
total += rects[i].area;
}
// Add a paint area for the page background (count 10% of the pixels not
// covered by existing paint rects.
var pixels = Math.max(doc.documentElement.clientWidth, win.innerWidth || 0) *
Math.max(doc.documentElement.clientHeight, win.innerHeight || 0);
if (pixels > 0 ) {
pixels = Math.max(pixels - total, 0) * pageBackgroundWeight;
if (paints[firstPaint] === undefined)
paints[firstPaint] = 0;
paints[firstPaint] += pixels;
total += pixels;
}
// Calculate the visual progress
if (total) {
for (var time in paints) {
if (paints.hasOwnProperty(time)) {
progress.push({'tm': time, 'area': paints[time]});
}
}
progress.sort(function(a,b){return a.tm - b.tm;});
var accumulated = 0;
for (var j = 0; j < progress.length; j++) {
accumulated += progress[j].area;
progress[j].progress = accumulated / total;
}
}
};
// Given the visual progress information, Calculate the speed index.
var CalculateSpeedIndex = function() {
if (progress.length) {
SpeedIndex = 0;
var lastTime = 0;
var lastProgress = 0;
for (var i = 0; i < progress.length; i++) {
var elapsed = progress[i].tm - lastTime;
if (elapsed > 0 && lastProgress < 1)
SpeedIndex += (1 - lastProgress) * elapsed;
lastTime = progress[i].tm;
lastProgress = progress[i].progress;
}
} else {
SpeedIndex = firstPaint;
}
};
/****************************************************************************
Main flow
****************************************************************************/
var rects = [];
var progress = [];
var firstPaint;
var SpeedIndex;
var pageBackgroundWeight = 0.1;
try {
var navStart = win.performance.timing.navigationStart;
GetRects();
GetRectTimings();
GetFirstPaint();
CalculateVisualProgress();
CalculateSpeedIndex();
} catch(e) {
}
/* Debug output for testing
var dbg = '';
dbg += "Paint Rects\n";
for (var i = 0; i < rects.length; i++)
dbg += '(' + rects[i].area + ') ' + rects[i].tm + ' - ' + rects[i].url + "\n";
dbg += "Visual Progress\n";
for (var i = 0; i < progress.length; i++)
dbg += '(' + progress[i].area + ') ' + progress[i].tm + ' - ' + progress[i].progress + "\n";
dbg += 'First Paint: ' + firstPaint + "\n";
dbg += 'Speed Index: ' + SpeedIndex + "\n";
console.log(dbg);
*/
return SpeedIndex;
};
// Testable addition to also get various other metrics
var PageSpeedMetrics = function() {
var answer = {
pageWeight: 0,
pageRequests: 0
};
var perfEntries = performance.getEntries();
for (var i = 0; i < perfEntries.length; i++) {
var entry = perfEntries[i];
if (entry.entryType === 'navigation' || entry.entryType === 'resource') {
answer.pageRequests++;
answer.pageWeight += entry.transferSize || 0;
}
if (entry.entryType === 'navigation') {
var connectStart = entry.connectStart || 0;
answer.firstByte = entry.responseStart - connectStart;
answer.firstInteractive = entry.domContentLoadedEventEnd - connectStart;
answer.pageLoadMs = entry.loadEventEnd - connectStart;
answer.url = entry.name;
} else if (entry.entryType === 'paint' && entry.name === 'first-paint') {
answer.firstPaint = entry.startTime;
} else if (entry.entryType === 'paint' && entry.name === 'first-contentful-paint') {
answer.firstContentfulPaint = entry.startTime;
}
}
if (!answer.url) {
var perfTiming = performance.timing;
answer.firstByte = perfTiming.responseStart - perfTiming.connectStart;
answer.firstInteractive = perfTiming.domContentLoadedEventEnd - perfTiming.connectStart;
answer.pageLoadMs = perfTiming.loadEventEnd - perfTiming.connectStart;
answer.url = window.location.href;
}
var memory = window.performance.memory;
if (memory) {
answer.jsHeapSizeLimit = memory.jsHeapSizeLimit;
answer.totalJSHeapSize = memory.totalJSHeapSize;
answer.usedJSHeapSize = memory.usedJSHeapSize;
}
return answer;
}
var answer = PageSpeedMetrics();
answer.speedIndex = RUMSpeedIndex(window);
return answer;
