Type of undefined in javascript? [closed]

Question

This is not a practical problem, I just need an explanation.

I have the following code:

var src = container.find('img').attr('src');
if(src === 'undefined') {
    alert('No src');
}

When i fire up the console and log the src it says it's undefined but the alert is not fired. Debugging this piece of code justifies previous behaviour. When i remove the '' in the if statement and leave undefined as a type, the alert gets triggered.

On the other hand, further down my code i have this piece:

var pathname = (window.location.pathname).split('/');
if(pathname[5] === 'undefined') {
    alert('Something...');
}

And the alert gets triggered properly whenever the console says that pathname[5] is undefined.

Therefore, i figured that in the first case undefined is returned as type and in the second as a string. Is this correct, and why such behaviour?

Thanks for all smart answers!

Answer 1

Since src has already has been declared all you need to do is check its truthyness:

if (!src) alert('no src');

If the variable can have a falsy value (empty string, zero, false) then you should check for both undefined and null like:

if (src === null || src === undefined)

Or taking advantage of type casting since null == undefined

if (src == null)