Benchmarking Array Initialization Methods: Why is [] Faster Than new Array?

When dealing with arrays in JavaScript, developers often face the dilemma of choosing between the shorthand syntax [] and the constructor-based approach new Array(). Recent testing has revealed that the former is significantly faster, leaving many wondering about the underlying reasons.

Understanding the behavior of the JavaScript engine sheds light on this discrepancy. During lexical analysis, a series of tokens is generated for the code, such as ARRAY_INIT and NEW. The ARRAY_INIT token directly leads to array creation, while NEW requires further processing to determine what action to take.

In the case of [], the engine immediately recognizes the intent to create an array. This eliminates the need for the additional tokenization, scope chain lookup, and constructor invocation required for new Array(). The constructor itself introduces further complexities, such as handling of variable argument lengths and type checking.

Consequently, [] emerges as the faster method, as it allows the engine to optimize the process by directly creating an array without the need for additional operations. This performance advantage is evident in benchmarks, where [] significantly outperforms new Array().