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JavaScript

Posted by jason chan
jason chan
31,009 Points

Someone walk me through this?

What does it output?

(function() {
  var a = b = 5;
})();

console.log(b);
// 5, but why?

2 Answers

jared eiseman
jared eiseman
29,023 Points
jared eiseman
jared eiseman
29,023 Points

if you console.log(a) it is also 5. So basically what this statement is saying is this:

I would like to create a variable, 'a', as well as a variable 'b'. 'a' should be equal to 'b', and 'b' is equal to 5, therefore 'a' is also equal to 5. Since it is all in the same statement (no semi-colons separating) the browser is processing it all at the same time, and is smart enough to figure out that the value it's assigning to both variables is 5.

Another way to write this, that is more legible would be:

var b = 5;
var a = b;

The whole "var a = b = 5;" thing is a pretty poor way of writing this, for future reference. If for nothing other than readability, the example I gave above is a more conventional way of writing it. Another example would be:

var b = 5,
    a = b;

Hope this is what you were looking for.

Craig Garner
Craig Garner
25,732 Points
Craig Garner
Craig Garner
25,732 Points

You have put the anonymous function in the global scope and it is automatically executed.