check if in set javascript code example

Example 1: javascript check if set

if (typeof variable !== 'undefined') {
    // the variable is defined
}
//or
if (typeof variable === 'undefined') {
    // variable is undefined
}

Example 2: javascript check if set contains

var mySet = new Set();
mySet.add('foo');

mySet.has('foo');  // returns true
mySet.has('bar');  // returns false

var set1 = new Set();
var obj1 = {'key1': 1};
set1.add(obj1);

set1.has(obj1);        // returns true
set1.has({'key1': 1}); // returns false because they are different object references
set1.add({'key1': 1}); // now set1 contains 2 entries