The method executeScript(selenium web driver) cannot define a global variable for later use?

Question

I am using the method executeScript in selenium web driver, I found a problem:

js.executeScript("var b='1'; ");
js.executeScript("alert(b)");

After I run above code, I suppose get a alert window with value is 1, but it says:

b is not defined

My question is: I defined b as a global variable, but why I cannot get it in later?

Answer 1

Defining a variable as

var b='1'

limits the scope to the execution of the script. Selenium wraps the execution of javascript snippets into their own script so your variable does not survive the end of the script. Try

window.b = '1';

and then later

alert(window.b);

to put the variable into global scope.