Does javascript not support tail recursion?

Tail recursion is an algorithm optimization technique that can transform a recursive algorithm into a more efficient iterative algorithm. Compared with conventional recursion, tail recursion can greatly reduce the depth of the stack, thereby avoiding problems such as stack overflow. However, JavaScript does not support tail recursion, which is a problem for many engineering practices.

Why doesn’t JavaScript support tail recursion?

In many programming languages, tail-recursive operations are automatically optimized into iterative operations by the interpreter or compiler. This is achieved through certain optimization techniques. However, JavaScript does not support this optimization, and converting tail recursion into iterative operations requires manually writing iteration code.

The JavaScript engine relies on script code written by JavaScript developers, and uses the calling mechanism and syntax parser developed by JavaScript developers to parse the code. Since the stack model used by the JavaScript engine is different from the stack models common in other languages, it is very difficult to implement tail recursion optimization.

Tail call and tail recursion

When learning JavaScript, you may often hear the concepts of "tail call optimization" and "tail recursion". Although these two concepts are very similar, they But it's different.

Tail call means that when the last statement of a function is a function call, the call of this function can be optimized by the compiler to "jump" to the sub-function for execution, which can avoid creating multiple frames and causing overhead, thereby reducing memory usage, which is also an optimization technique.

Tail recursion is a special tail call. Recursion is when a function calls itself during execution. If the recursion is tail recursion, then this recursive call must be the last statement of the function, that is, no additional operations are required. It only needs to convert the function call and parameter transfer into an instruction, and then jump to the beginning of the function.

Tail recursion example

The following is a classic, recursive implementation of factorial:

function factorial(n) {
  if (n === 1) return 1;
  return n * factorial(n - 1);
}

At this time, we will call it recursively n times, and it will be on the stack Leave n function call records. When the factorial number is large, you will face the problem of stack overflow.

Modify the above code to implement tail recursion:

function factorial(n, sum = 1) {
  if (n === 1) return sum;
  return factorial(n - 1, n * sum);
}

In this function, the sum variable records the intermediate result of the factorial. The factorial of a number can be calculated by multiplying it with the previous number. Calculation, there is no need to calculate the factorial of each number and then multiply them. We pass this intermediate result as a parameter to the next recursion, thus achieving tail recursion optimization.

Conclusion

The JavaScript engine does not support tail recursive optimization, which has certain limitations for developers. Developers must manually convert to an iterative algorithm, or implement tail recursion in another language. If you need to use tail recursion in actual work, you can use solutions such as manually simulating the call stack to achieve the effect.

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