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What is IIFE in JavaScript?

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二04 | 时间 2018 | 作者 红领巾 ] 0人收藏点击收藏

The first time I heard 'IIFE' in my Coding Bootcamp class, it immediately reminded me of my sister's dog 'Yeffi' which means 'pretty' in some human language.

So what is IIFE in javascript language?

IIFE stands for Immediately Invoked Function Expression. It is a JavaScript function that runs as soon as it is defined.

Normally, when we create a function using 'Function Declaration' or 'Function Expression', we need to call the function in order to use it.

Function Declaration: function myFunction(p1, p2) { return p1 * p2; } alert(myFunction(4, 3)); //12 Function Expression: let myFunction = function(p1, p2){ return p1 * p2; } alert(myFunction(4,3)); //12

However, in IIFE, the function is wrapped in a parenthesis which makes it a function expression followed by () which tells the JavasScript compiler to invoke or call immediately.

(function() { let dName = "Yeffi"; alert(dName); } )(); //Yeffi

So why do we use IIFE?

Mainly because of privacy. Any variables declared inside the IIFE are not visible to the outside world.

(function() { let dName = "Yeffi"; } )(); console.log(dName); // Uncaught ReferenceError: dName is not defined

We can’t access the dName variable outside of the IIFE. All of the code within our IIFE stays within the private scope of our function.

Also, it protects the global namespace by not creating a named function. When the named function hangs around, it could accidentally be invoked again, but IIFE isn't named so it can't accidentally be called. This will avoid any potential security implications. Therefore, many JavaScript libraries use this technique nowadays.

Thanks for reading!

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