如何检查不存在的班级？ （getElementsByClassName）

Question

arr = document.getElementsByClassName(type2);  // suppose type2 is not available in the dom - class = "some_class"
// check for empty

This snippet returns

[object HTMLCollection]

which has a length of 0.

Is this the best way to check for the class not existing when getElementsByClassName is used, ie, just check for a length of 0?

Answer 1

Yes. Check the length property of the returned collection.

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Since 0 is falsy, you can do this:

var type2 = 'some_class';
var noElementHasType2Class = ! document.getElementsByClassName(type2).length;