Eloquent JavaScript: Can't understand recursion example -

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• how eloquent javascript recursion example terminate return 1 still output exponential value 2 answers

from page 50 of haverbeke's second edition. added couple of console.log try better track progress.

function power(base, exponent) {   if (exponent == 0) {     console.log("line 5 " + base + "  " + exponent);      return 1;   }   else     console.log("line 10 " + base + "  " + exponent);     return base * power(base, exponent -1); } console.log(power(2,3)); 

// output

line 10 2  3  line 10 2  2  line 10 2  1  line 5 2  0  8 

//

i expect final output 1 since when if (exponent == 0) true, next statement return 1;, appears enter else 1 more time return 8. shouldn't return kick out of function.

obviously newbie or wouldn't stuck on page 50 of supposedly beginner book.

thanks help.

whenever function enters "else" branch, new stack frame created, waiting result of recursive call. can imagine evaluation step step:

1. power(2, 3) enters else branch, , returns base * power(base, exponent - 1).

2. 2 * power (2, 2) enters else branch, , returns base * power(base, exponent - 1).

3. 2 * (2 * power (2, 1)) enters else branch, , returns base * power(base, exponent - 1).

4. 2 * (2 * (2 * power (2, 0))) enters if branch, , returns 1.

5. you can evaluate result: 2 * (2 * (2 * 1)), 8.