rauschma

Strings

String.prototype.*

None of the string methods modify this – they always return fresh strings.

• charAt(pos: number): string ^ES1

  Returns the character at index pos, as a string (JavaScript does not have a datatype for characters). str[i] is equivalent to str.charAt(i) and more concise (caveat: may not work on old engines).

paulirish

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

• elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

ebidel

// Know how fast your HTML Imports are.
// crbug.com/505279 - doesn't show sub-import resources.
var imports = document.querySelectorAll('link[rel="import"]');
[].forEach.call(imports, function(link) {
  var entries = performance.getEntriesByName(link.href);
  console.info('=== HTML Imports perf ===');
  entries.forEach(function(e) {
    console.log(e.name, 'took', e.duration, 'ms');
  });
});