Why is Array Initialization Faster with [] than new Array()?

Faster Array Initialization: [] vs new Array()

Question: Why does using [] to initialize an array perform faster than using new Array()?

Answer:

Beyond previous responses, let's examine this from a compiler's perspective:

1. Tokenization:

   • []: Indicates an array initialization (e.g. arr = [];).
   • new Array: Multiple tokens denoting a function call (e.g. var arr = new Array();).

2. Object Creation:

   • []: Leads directly to array creation.
   • new Array: Requires constructor invocation, checking for arguments, and potentially performing additional type checks.

3. Function Calls:

   • []: No function call overhead.
   • new Array: Invokes a constructor, which is generally slower than direct object creation.

4. Ambiguity:

   • []: Unambiguously indicates array initialization.
   • new Array: Requires the JavaScript VM to determine the specific action (e.g., new keyword, Array identifier).

5. Overloading:

   • []: Always creates an array.
   • new Array: Can behave differently depending on the number of arguments provided. This adds further complexity and overhead during object creation.

In summary, using [] for array initialization is faster because it skips the additional processing, function invocation, and ambiguity resolution required by new Array. The compiler can directly create an array without requiring the VM to perform these extra steps.

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