What's the Difference Between a Function Call and a Function Reference in JavaScript?

Distinguishing Function Calls from Function References

When working with functions in JavaScript, understanding the difference between a function call and a function reference is crucial. While both concepts involve functions, they serve distinct purposes.

Function Call

A function call executes a function immediately. It involves specifying the function name followed by parentheses. For example:

function hello() {
  alert("hi!");
}

hello(); // Function call

Function Reference

In contrast, a function reference does not execute the function immediately. It instead assigns the function to a variable or an event listener. This allows the function to be executed later when necessary. For example:

var elem = document.getElementById("btn");
elem.onclick = hello; // Function reference

In this code snippet, the onclick property of the elem element is assigned a reference to the hello function. When the element is clicked, it will trigger the execution of the hello function.

Determining When to Use a Reference

The use of a function reference is necessary in situations where the function should be executed later or when it is assigned to an event. Common scenarios include:

• Event listeners: Event listeners, such as onclick, onmouseover, and onkeydown, expect a function reference to be executed when a specific event occurs.
• Callbacks: Functions that are passed as arguments to other functions often require a function reference to be executed later.
• Variable assignments: Functions can be assigned to variables to be called later or passed to other functions.

Important Note

It's crucial to avoid calling the function when assigning it to a reference. Adding parentheses, like funcRef(), will execute the function immediately and assign its return value, which may not be the desired outcome. Instead, the function should be assigned as a reference without parentheses.

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