Question

var boolTrue = true;
var randomObject;

if (boolTrue)
// this will fire

if (randomObject)
// this will fire, because the object is defined

if (!objectNotDefined)
// this will fire, because there is no defined object named 'objectNotDefined'

Coming from a C++ and C# background, I am very familiar with the basic if(expression) syntax. However, I think it is not very readable to have both expressions (true/false) and have object existence also being a expression. Because now if I see a function like below, i don’t know if the data coming in is an object (existence/undefined check) or a boolean.

function(data) {
   if (data)
      // is this checking if the object is true/false or if the object is in existence?
}

Is this just the way it is? I mean, is there anyway to easily read this? Also, where is this documented anywhere in the JS spec (curious)?

Answer 1

In Javascript everything is “true” (or “truthy” to be more precise using Javascript parlance) except false, 0, undefined, null, NaN and empty string.

To avoid confusion use:

 if (data === true) // Is it really true?

and

if (typeof data === 'undefined') // Is the variable undefined?