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The Speed Advantage of Array Literals: [] vs. new Array
When creating arrays in JavaScript, using the array literal notation ([]) offers a significant performance boost compared to the new Array() syntax. Multiple benchmarks have demonstrated this efficiency, with [] consistently outperforming new Array().
Why [] Executes Faster
- Fewer Tokenization Steps: The lexical analysis phase for [] is straightforward, producing ARRAY_INIT tokens that directly map to array creation. In contrast, new Array requires additional tokenization steps to identify the new keyword, Array identifier, and function call.
- No Scope Lookup: With [], the interpreter knows immediately that an array is being created. On the other hand, new Array() triggers a scope lookup for the Array identifier, which slows down execution.
- Function Call Overhead: new Array() is an implicit function call, while [] is not. Function calls have inherent performance implications due to parameter checking and activation object creation.
- Constructor Logic: The Array constructor is overloaded, requiring additional checks for argument length and type. [] bypasses these checks as it is a direct array literal.
Performance Impact
Benchmarks have shown that [] can be approximately 20% faster than new Array(). This efficiency is particularly noticeable in loops or other sections of code that create a large number of arrays.
Conclusion
When creating arrays in JavaScript, opting for the array literal syntax [] is recommended for better performance. This shortcut eliminates unnecessary tokenization steps, scope lookups, and function call overhead, resulting in faster array creation and overall code execution.
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