Is a string of whitespace truthy or falsy in JavaScript?

Is a string of whitespace truthy or falsy?

It's truthy, as others indicated. However, your comparsion

' ' == true

is not checking whether ' ' is truthy. It's comparing two values, which is a different thing and uses specific comparison rules. The JS spec is that any == comparison with a boolean first coerces the boolean to a number:

If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).

So your code is equivalent to

' ' == Number(true)

which is the same as

' ' == 1

Next, to compare a string and a number, JS converts the string to a number. Again, quoting the spec:

If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x) == y.

So we now have

Number(' ') == 1

Number(' ') is 0. The spec says:

The MV of StringNumericLiteral ::: StrWhiteSpace is 0.

So this becomes

0 == 1

which, as you found, is false. See http://ecma262-5.com/ELS5_HTML.htm#Section_11.9.3 for details.

As other answers have explained not being equal (==) to true is not the same as being falsy. Falsy is a different concept, which roughly means the value to which an expression is coerced when a boolean is required (such as the condition of an if statement) is false.

The string ' ' is a "truthy" value.

Here is a list of the "falsy" values:

false
null
undefined
0
NaN
''

You have to understand that "truthy" is not the same thing as true. A value can be "truthy" without being true. For example, if we did 5 == true, we would get false, even though 5 is a "truthy" value.

In general, pretty much every value is "truthy" (excluding the ones mentioned above). But, the easiest way to check if something is "truthy"/"falsy" is by doing something like this:

var value = valueToTest;

if (value) {
  console.log('Truthy!');
} else {
  console.log('Falsy!');
}