Using an Anonymous Function to Wrap Global Variables
Problem
You need to create a variable that maintains state between function calls, but you want to avoid global variables.
Solution
Use an Immediately-Invoked Function Expression (IIFE) to wrap variables and functions
both:
<!DOCTYPE html>
<head>
<title>faux Global</title>
<script>
(function() {
var i = 0;
function increment() {
i++;
alert("value is " + i);
}
function runIncrement() {
while (i < 5) {
increment();
}
}
window.onload=function() {
runIncrement();
}
})();
</script>
</head>
<body>
</body>
</html>
EXPLAIN
An anonymous function surrounds the global values, is immediately evaluated, and
then never evaluated again. Ben Allam gave the pattern the name of ImmediatelyInvoked Function Expression (IIFE or “iffy”), though functionality demonstrated in the
solution has existed for some time. IIFEs are used in many major libraries and frame‐
works, including the popular jQuery, as a way of wrapping plug-in functions so that the
code can use the jQuery dollar sign function ($) when the jQuery plug-in is used with
another framework library.
The approach consists of surrounding the code block with parentheses, beginning with
the anonymous function syntax, and following up with the code block and then the final
function closure. It could be the following, if there’s no parameter passed into the code
block:
})();
or the following, if you are passing a parameter into the function:
})(jQuery);
Now you can create as many variables as you need without polluting the global space or colliding with global variables used in other libraries.
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