JavaScript 递归 function 在分配给变量时如何工作？

Question

Hi I am new to JavaScript but i don't understand how recursive function works when assigned to a variable. Below code should have only two outputs but instead it has 3 output.

 function capitalizeFirst(array) { if (array.length === 1) { return [array[0][0].toUpperCase() + array[0].substr(1)]; } const res = capitalizeFirst(array.slice(0, -1)); console.log(res); return res; } console.log(capitalizeFirst(['car', 'taco', 'banana']));

As I think: first capitalizeFirst(array.slice(0, -1)); will work as recursive function and return ['Car'] as result to res, then console.log(res) print result then return statement return res to function so final console.log(capitalizeFirst(['car', 'taco', 'banana'])); should return ['car'] as a result. So in console screen I should get two output but instead I am getting three why?

Answer 1

TLDR : Your recursive function outputs the first element of the array as a capitalized word equal to the length of your array - 1 AND this result is outputted. The total outputs being equal to the array length.

Your array has a length of 3 and in your base case will return an array. So res will be outputted 2 times within the recursive function and once outside.

If you have an array that is just [Car] , then the recursive function will return [Car] which will be outputted.

If you have an array that is [car, taco] , it will first go through the recursive function, then shrink down to [Car] and since this is the base case, will return [Car] . This means that within the recursive function, res = [Car] . And since you have console.log(res) and return res , [Car] will be outputted within the recursive function and then outputted outside.

In the scenario with an array length of 3, it will output [Car] twice within since the recursive function continues until the length is 1 (Meaning that it will hit the console.log twice). And finally when res is returned, it is [Car] which will be outputted by the outside console.log .