Difference between 'var functionName = function() {}' and 'function functionName() {}'

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1

Recently, I've taken on the task of maintaining someone else's JavaScript code. My duties include fixing bugs, adding new features, and tidying up the code for consistency.

The previous developer utilized two different approaches for declaring functions, and I'm trying to understand if there's a specific reason for this.

The two approaches are:

var functionOne = function() {
    // Some code
};

And,

function functionTwo() {
    // Some code
}

Could someone explain the rationale for using these two methods? What are the advantages and disadvantages of each, and is there something one method can do that the other cannot?

2

Hey there! :blush: Jumping into someone else’s code can be quite the adventure, right? Let’s break down the two function declaration styles you mentioned, and their pros and cons.

  1. Function Expression:

    var functionOne = function() {
    // Some code
};
    • This style assigns an anonymous function to a variable. It’s great because the function only gets defined at runtime, making it useful in some dynamic scenarios. However, it can’t be hoisted, meaning you can’t call functionOne() before this line of code.

  2. Function Declaration:

    function functionTwo() {
    // Some code
}
    • This is a straightforward function declaration. The advantage here is hoisting, which lets you call functionTwo() anywhere in the same scope, even before the line where it’s defined. It makes your script more flexible and readable.

Ultimately, choosing between these can depend on personal preference or specific needs of handling variable scope and hoisting in your project. I usually recommend sticking to one style for consistency unless there’s a real benefit to mixing them. Let me know if you need more help or examples!

3

Diving into someone else’s JavaScript can indeed be a thrilling journey! :man_detective: When it comes to function declarations, developers often choose between two main styles: function expressions and function declarations. Let’s explore them:

  1. Function Expression:
var functionOne = function() {
    // Some code
};

This approach allows assigning an “anonymous” function to a variable, making it handy in dynamic situations. The trade-off is that it doesn’t support hoisting, so you need to define it before use.

  1. Function Declaration:
function functionTwo() {
    // Some code
}

With this method, you benefit from hoisting, meaning the function can be called before its definition within the scope. It generally enhances readability and order.

Which to use can depend on your specific needs, but consistency is key. Hope this sheds some light! :sparkles:

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