Truthiness in ES5

Define 'truthy'

Here's a function we will use. It should already be defined in the Javascript console.

      function truthy(x) {
        return (x) ? true : false;
      }
    

Most values behave how you would expect

For example...

These values are all truthy

• > true

• > 1

• > 'false'

• > Infinity

• > -Infinity

These values are not truthy

• > false

• > 0

• > NaN

• > undefined

• > null

Things that make you go, "hmm"

• > ''

• > -1

• > {}

• > []

• > [0]

• > [null]

Where things go wack

Equals

==

Strict Equals

===

TL;DR

Always, always use strict equals.

Otherwise....

Tragedy Ensuses

A Test

    truthy([]); // => true
    truthy([] == false); // true
  

But wait...

    truthy(null);   // => false
    truthy([null]); // => true
    truthy([null] == false); // ?
  

And...

    truthy(0);   // => false
    truthy([0]); // => true
    truthy([0] == false); // ?
  

And...

    truthy(undefined);   // => false
    truthy([undefined]); // => true
    truthy([undefined] == false); // ?
  

But there's this...

    truthy([undefined] == [undefined]);
    truthy([undefined] == undefined);
  

And this...

    truthy([null] == [null]);
    truthy([null] == null);
    truthy([null] == 0);
    truthy([null] == '');
    truthy([null] == false);
  

And this...

    truthy([0] == [0]);
    truthy([0] == 0);
    truthy([0] == '0');
  

And this...

    truthy([Infinity] == [Infinity]);
    truthy([Infinity] == Infinity);
  

The concept of truthiness in Javascript is not that hard to deal with. But no matter what you do, always, always, always use strict equals. Because == can make you gaggy.