Functions as Data in JavaScript

Functions in JavaScript are objects and can therefore be used as data. Here are a few examples:

1. Assigning a function to a variable:

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let greet = function() {
    console.log("Hello, World!");
};

greet(); // Outputs: Hello, World!

In this example, we assign a function to the variable greet. We can then invoke the function using the variable name.

2. Storing functions in an array:

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let functionArray = [
    function() { console.log("Hello"); },
    function() { console.log("World"); }
];

functionArray[0](); // Outputs: Hello
functionArray[1](); // Outputs: World

Here, we have an array functionArray containing two functions. We can access and execute these functions using their index in the array.

3. Using functions as object properties (methods):

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let obj = {
    sayHello: function() {
        console.log("Hello");
    }
};

obj.sayHello(); // Outputs: Hello

In this example, we’re using a function as a method of an object. We can then invoke this method using dot notation.

4. Passing functions as arguments:

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function executeFunction(fn) {
    fn();
}

executeFunction(function() { console.log("Hello, World!"); }); // Outputs: Hello, World!

In this example, we pass a function as an argument to another function and execute it within that function.

5. Returning a function from a function:

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function getGreeter() {
    return function() {
        console.log("Hello, World!");
    }
}

let greeter = getGreeter();
greeter(); // Outputs: Hello, World!

In this example, a function getGreeter is returning another function. We can then store the returned function in a variable and invoke it later.

These examples illustrate that functions in JavaScript can be used as data, which can be assigned to variables, stored in data structures, passed as arguments to other functions, and returned as values from other functions. This feature provides a lot of flexibility in writing JavaScript code.