Falsey values in JavaScript

Question

I had an interesting interview question today that stumped me a little. I was asked about falsey values. So undefined, NaN, null, 0, and an empty string all evaluate to fals

Answer 1

It's important to understand how this works in JS, so you're not surprised. Not necessarily just what is falsey, but what is truthy and how they compare to each other.

One example is that '0' is considered equal to 0 with ==, but it is not equal to '' - though 0 is. JavaScript comparison isn't always transitive.

So this means that just because (foo==bar && bar==fizz) is true, (foo==fizz) is not always true. To go with the above example, '0'==0, and 0=='', but '0'!='' - because you're comparing strings in the latter instance, so they are compared as strings and not coerced to numbers.