Can someone help me explain why:
#id .classname
is worse than:
#id element.classname
from a rendering/performance perspective?
Can someone help me explain why: #id .classname is worse than: #id element.classname from
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Can someone help me explain why:
#id .classname
is worse than:
#id element.classname
from a rendering/performance perspective?
Because the DOM has special functions (
getElementByTagName) dedicated to find all elements in a tree by their tag name. These functions use lookup tables and are well optimized. No such method exist for classnames, however, and finding a classname requires to iterate through all the tree(s) and check existing classnames. This algorithm can be made quicker by reducing the size of the trees to iterate, and using anelement.prefix does just this: it reduces the size of the trees to look for the classname.