js-under-pressure.js

// DISCLAIMER: This is not necessarily good code. It’s just code that I wrote 
// as quickly as possible to do each task.

// 1

return 2*i;

// 2

return !(i%2);

// 3

return (i.match(/\.(.+)$/) || [,false])[1];

// 4

var l = '';
for (var n=0; n<i.length; n++)  {
	if (typeof i[n] == 'string' && i[n].length > l.length) {
	    l = i[n];
	}
}
return l;

// 5

function arraySum(a) {
	var sum = 0;
	for (var i=0; i<a.length; i++) {
		var n = a[i];
		if (n === +n) {
			sum += n;
		}
		else if (Array.isArray(n)) {
			sum += arraySum(n);
		}
	}
	return sum;
}