Default Parameters in ES6

function defaultFunc(x = 1, y = 2, z = 3) {
    console.log(x, y, z);
}

defaultFunc(5);
defaultFunc(5, 6);
defaultFunc(undefined, 6, 7);

function getData(data, useCache = true) {
    if (useCache) {
        console.log('using cache for', data);
    }
    else {
        console.log('not using cache', data);
    }
}

getData('abc');
getData('def', false);

Output

5 2 3 
5 6 3 
1 6 7 
using cache for abc 
not using cache def