**Spread Syntax vs. Rest Parameter: What\'s the Difference?**

Spread Syntax and Rest Parameter in ES2015 / ES6

In JavaScript, the spread syntax (...) and the rest parameter (...) have introduced new ways to work with arrays and function parameters. They can seem similar, but understanding their distinct roles is crucial for effective coding practices.

Spread Syntax: Expanding Arrays

Spread syntax expands an existing array into individual elements within a new array. For instance, let's consider two arrays, abc and def:

<code class="js">var abc = ['a', 'b', 'c'];
var def = ['d', 'e', 'f'];</code>

By using spread syntax with the ... operator on these arrays, we can create a new array alpha that includes elements from both:

<code class="js">var alpha = [ ...abc, ...def ];</code>

The result will be:

<code class="js">alpha == ['a', 'b', 'c', 'd', 'e', 'f'];</code>

In this example, spread syntax expands the arrays abc and def into their individual elements, effectively creating a larger array.

Rest Parameter: Collecting Arguments

On the other hand, the rest parameter collects multiple arguments into a single array. It is typically used in function definitions.

<code class="js">function sum(...numbers) {
  // numbers will contain an array of all arguments passed to the function
}</code>

When calling this function, all arguments are captured as an array within the numbers parameter:

<code class="js">sum(1, 2, 3, 4, 5); // numbers == [1, 2, 3, 4, 5]</code>

The rest parameter is commonly used to handle variable-length function arguments, simplifying the processing of multiple values.

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