Use .has and .size on an ES6 Set

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Let's look at the .has and .size methods available on the ES6 Set object.

First, create an ES6 Set

var set = new Set([1, 2, 3]);

The .has method will check if the value is contained within the set.

var hasTwo = set.has(2);

The .size method will return an integer representing the size of the Set

var howBig = set.size;