HTML DOM查找的时间复杂度是多少? [英] What is the time complexity of HTML DOM lookups
问题描述
我在说生气,讨厌,不要打破't-fix-it,ie v6 javascript,cost。
下限为:
document.getElementById()
与
document.getElementsByTagName('div')查找。
getElementById
可以在现代浏览器中安全地假定为 O(1)
,因为散列表是id =>元素映射的完美数据结构。
没有任何优化,任何简单的查询 - 无论是css选择器,id查找,类还是标签名称查找 - 都不比 O(n)
因为所有元素的迭代总是足够的。
然而,在一个好的浏览器中,我希望它有一个tagname =>元素映射,所以 getElementsByTagName
也将是 O(1)
Assuming there are no crazy optimizations (I'm looking at you Chrome).
I'm talking about raw, nasty, ain't-broke-don't-fix-it, ie v6 javascript, cost.
The lower limit being:
document.getElementById()
Versus:
document.getElementsByTagName('div') lookup.
getElementById
can safely assumed to be O(1)
in a modern browser as a hashtable is the perfect data structure for the id=>element mapping.
Without any optimizations any simply query - be it a css selector, an id lookup, a class or tag name lookup - is not worse than O(n)
since one iteration over all elements is always enough.
However, in a good browser I'd expect it to have a tagname=>elements mapping, so getElementsByTagName
would be O(1)
too.
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