[1,2, 3, 4, 5].indexOf(4) !== -1 [1,2, 3, 4, 5].filter(a=> a ===4).length > 0 [1,2, 3, 4, 5].find(a => a === 4) !== undefined [1,2, 3, 4, 5].some( a => a === 4) ![1,2, 3, 4, 5].every( a => a !== 4) [1,2, 3, 4, 5].lastIndexOf(4) !== -1 [1,2, 3, 4, 5].includes(4)

test

Performance comparison of two methods of combining arrays shown here: https://twitter.com/SimonHoiberg/status/1287797397137965057

xcbdfb

test querySelector by tag against ID when only one element of that tag name exists

For in vs object keys test

For in vs object keys