Return statement inside if statement ignores variable it should return

August 23, 2023

I have a little calculator app.

The return statement is inside of an if statement checking for a variable to be equal to "null". If the variable is equal to "null", it should return the input the function is called with. However, it always returns undefined, no matter what the input is.

Here is the code:

const input = ['1', 'substract', '3'];

const findNextOperation = (input) => {
    let operation;
    let ind;

    //First * or /
    ind = input.findIndex(el => /multiply|divide/.test(el));

    //Then + or -
    if (ind === -1) ind = input.findIndex(el => /add|substract/.test(el));

    //No operations left
    if (ind === -1) return null;

    operation = input[ind];
    return { operation, ind };
}

const performOperation = (a, b, operation) => {
    a = Number(a);
    b = Number(b);

    switch (operation) {
        case 'add':
            return a + b;
        case 'substract':
            return a - b;
        case 'multiply':
            return a * b;
        case 'divide':
            return a / b;
        default:
            return;
    }
}

const calculate = (input) => {
    const operation = findNextOperation(input);
    if (operation === null) {
        console.log('here', input[0]) // Logs "here -2" to the console
        return input[0]; // Returns "undefined"
    }

    const operationOutcome = performOperation(input[operation.ind - 1], input[operation.ind + 1], operation.operation);
    calculate(input.toSpliced(operation.ind - 1, 3, operationOutcome));
}

console.log(calculate(input)); // Logs "undefined" to the console

I can’t figure out where it goes wrong.

Edit: I didn’t know that was a thing with recursive functions. mb

>Solution :

You’ve made a recursive approach by calling calculate in the calculate function.

However, the return value of the second call is lost.

You should change the following

calculate(input.toSpliced(...

// to

return calculate(input.toSpliced(...

const findNextOperation = (input) => {
    let operation;
    let ind;

    //First * or /
    ind = input.findIndex(el => /multiply|divide/.test(el));

    //Then + or -
    if (ind === -1) ind = input.findIndex(el => /add|substract/.test(el));

    //No operations left
    if (ind === -1) return null;

    operation = input[ind];
    return { operation, ind };
}

const performOperation = (a, b, operation) => {
    a = Number(a);
    b = Number(b);

    switch (operation) {
        case 'add':
            return a + b;
        case 'substract':
            return a - b;
        case 'multiply':
            return a * b;
        case 'divide':
            return a / b;
        default:
            return;
    }
}

const calculate = (input) => {
    const operation = findNextOperation(input);
    if (operation === null) {
        return input[0]; // Returns "undefined"
    }

    const operationOutcome = performOperation(input[operation.ind - 1], input[operation.ind + 1], operation.operation);
    return calculate(input.toSpliced(operation.ind - 1, 3, operationOutcome));
}

console.log(calculate(['1', 'substract', '3']));
console.log(calculate(['10', 'divide', '3']));