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问题:
My code to set a global variable using eval is not working. It's as if the assignment is not called at all, but no script errors occur.
Click to see 'x'
When the page loads, the alert shows what I expect; it confirms that x = 1. But after that, I click on the div and get a javascript error that x is undefined. How do I make eval add this variable properly?
Background: The code above is a minimally reproducing example from a project I'm working on where we must execute javascript code during AJAX responses. eval works properly most of the time, but this is causing problems.
回答1:
Eval runs locally, you're setting a local variable.
To set a global variable, remove var;
回答2:
You could use window.eval() to run eval() from global scope. This will assign var as a variable of window, which is what a global variable is: a variable attached to window.
... But you really really shouldn't. eval() is sandboxed for a reason.
That is not unless you really know what you are doing and trust everything you are receiving through XMLHttpRequest. It is one of those chicken/egg things: if you trust the code enough to execute it, it should be programmed well enough to prefix global variables with window. to begin with; thus, you should not need to use window.eval().
Besides, unless you are just trying to avoid async headaches by using the more-manageable XMLHttpRequest (there's a first time for everything...), you really should just create a script tag, assign it's source, and append it as a child to the head or body tag. Dynamically appending script tags is even faster than using XHR, especially for big scripts.
回答3:
I wouldn't recommend setting global variables, but if you absolutely have to, use the window object:
window['x'] = 1;
