allEqual

Checks if all elements in an array are equal.

• Use Array.prototype.every() to check if all the elements of the array are the same as the first one.
• Elements in the array are compared using the strict comparison operator, which does not account for NaN self-inequality.

const allEqual = arr => arr.every(val => val === arr[0]);

allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true