Is Caching Array Length Faster than Direct Length Access in JavaScript?

Optimizing Array Iteration in JavaScript: Caching Length vs. Direct Length Access

Looping through arrays is a fundamental operation in JavaScript. But what's the quickest approach? Conventional wisdom has held that caching the array's length improves performance by avoiding repeated calculations. However, some argue that modern compilers optimize direct length access.

The Debate: Caching vs. Direct Access

Traditionally, the recommended approach was to cache the array length:

<code class="javascript">for (var i = 0, len = arr.length; i < len; i++) {
  // Perform operations
}</code>

This method stores the array length in a local variable len to avoid calculating it repeatedly within the loop.

Others contend that compilers optimize direct length access, rendering caching superfluous:

<code class="javascript">for (var i = 0; i < arr.length; i++) {
  // Perform operations
}</code>

Benchmarking Results

To determine the most efficient approach, a benchmark test was conducted across various modern browsers: https://jsben.ch/wY5fo.

Conclusion: Caching Length Emerges Victorious

Despite arguments for direct length access, the benchmark results suggest that caching the array's length remains the fastest method in practice. This is likely due to optimizations made by JavaScript engines, which prioritize clarity over cleverness.

Therefore, the recommended approach for looping through arrays in JavaScript is to utilize the standard for-loop with length caching:

<code class="javascript">var i = 0, len = myArray.length;
while (i < len) {
  // Perform operations
  i++;
}</code>

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