While loop inside recursive function failed if looped more than once

Question

My code below runs fine if the while loop condition is < 6 (i.e. one loop), but failed if it is set to < 7 or more (i.e. more than 1 loop)

var data = {
    a: "abc",
    c: 0
}

function recurse(data, nodes) {
    const first = nodes.shift();
    console.log("first-"+first.id, first.t);

    if (first.t == "action") {
        data.c = data.c + 1;
        console.log("exec action", data.c);
    } else {
        switch (first.t) {
            case "if_else":
                console.log(recurse(data, first.b[0].actions), 300);
                break
            case "while":
                var brNodes = first.b[0].actions
                while (data.c < 7) {
                  console.log(recurse(data, brNodes), 400);
                }
                break
            default:
                break
        }
    }
    
    return (nodes.length > 0)? console.log(recurse(data, nodes), 200): "Completed"
} 

var actions = [
    {id:1, t:"action", b:null},
    {id:2, t:"action", b:null},
    {id:3, t:"if_else", b:[{id:31, t:"branch", actions:[{id:311, t:"action", b:null}, {id:312, t:"action", b:null}]},{id:32, t:"branch", actions:[{id:321, t:"action", b:null}]}]},
    {id:4, t:"action", b: null},
    {id:5, t:"while", b:[{id:500, t:"branch", actions:[{id:511, t:"action", b:null}]}]},
    {id:6, t:"action", b:null}
]

console.log(recurse(data, actions), 100)

Here is my testing on StackBlitz https://stackblitz.com/edit/recurse?file=index.js

@ManuelSpigolon - data and data.c are defined at the beginning of the OP's code block. — jfriend00
– jfriend00, Commented Nov 9, 2020 at 15:06

Kk Gan · Accepted Answer · 2020-11-09 16:12:34Z

1

looks like i have figured it out myself... the array was passed in by reference, and after the first loop it was consumed to an empty array. i replaced it with [...] spread

console.log(recurse(data, [...first.b[0].actions]), 400);

and this should solved

answered Nov 9, 2020 at 16:12

Kk Gan

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jfriend00 · Accepted Answer · 2020-11-09 15:05:43Z

0

Your code is doing this:

const first = nodes.shift();

And, then attempting to access:

 first.b[0].actions

And, nodes.shift() removes the first element from the nodes array. Your nodes array has 6 items. If you try to call your function 7 times by setting the condition to while (data.c < 7), you will end up with an empty nodes array and thus an undefined value in first on the last iteration and that will cause an error when your code attempts to access first.b[0].actions on the last iteration.

answered Nov 9, 2020 at 15:05

jfriend00

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1 Comment

jfriend00 Over a year ago

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