Spread Syntax vs. SpreadElement in ECMAScript: What's the Difference?

Spread Syntax vs SpreadElement in ECMAScript

Overview

The ECMAScript specification and MDN documentation both mention the concept of "spread," but these terms refer to different entities.

Spread Syntax in MDN

MDN's Spread syntax enables the expansion of iterable objects (such as arrays or strings) into places where zero or more arguments are expected (function calls) or elements (array literals). It uses the ... syntax.

SpreadElement in ECMAScript

In the ECMAScript documentation, the SpreadElement is described as part of the syntax for:

...AssignmentExpression[In, ?Yield]

This syntactic construct represents the spreading of an iterable into an array during assignment operations. Essentially, it performs an in-place array concatenation.

Differences between SpreadElement and Spread Syntax

SpreadElement and Spread syntax are different terms for related concepts:

• SpreadElement: A specific syntactic construct in ECMAScript that expands an iterable into an array during assignment.

• Spread syntax: A generic term that encompasses both SpreadElement and other spread constructs, including:

  • Rest parameters (functions)
  • Rest elements (destructuring)
  • Spread arguments (function calls)

Use Cases

Use Cases of SpreadElement:

• Concatenating arrays
• Creating copies of arrays without modifying the original
• Passing iterable objects as parameters in-place

Use Cases of Spread Syntax:

• Function calls: Passing multiple arguments as an iterable
• Array literals: Creating arrays from iterables
• Object literals: Spreading objects with key-value pairs
• Rest parameters: Collecting remaining arguments in a function
• Rest elements: Collecting remaining values in a destructuring assignment

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