Set.prototype.size

Size属性将会返回Set对象中元素的个数。

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size的值是一个整数，表示Set对象有多少条目。size的集合访问函数是undefined; 你不能改变这个属性。

var mySet = new Set();
mySet.add(1);
mySet.add(5);
mySet.add("some text")

mySet.size; // 3

• Set