How to Interrupt a Node.js forEach Loop

In situations where you need to traverse nested data structures recursively and execute an operation for each element, you might use a combination of recursion and forEach. However, there may be instances where you need to prematurely exit the forEach loop.

Unlike a regular loop with break or continue statements, forEach lacks a built-in mechanism to halt its iteration. To simulate this behavior, let's explore three approaches:

1. The "Ugly" Way: Using a Contextual Boolean

Pass a second argument to forEach as the context and store a boolean value in it. Inside the callback function, check the boolean and break out if necessary. This approach is visually unappealing.

function recurs(comment) {
    var stop = false;
    comment.comments.forEach(function (elem) {
        recurs(elem);
        if (...) stop = true;
    }, stop);
}

2. The "Controversial" Way: Exception Handling

Enclose the forEach loop within a try-catch block. When you want to break, throw an exception and catch it outside the loop. This approach can impact performance and may raise concerns about code readability.

try {
    comment.comments.forEach(function (elem) {
        recurs(elem);
        if (...) throw new Error("Stop Iteration");
    });
} catch (e) {
    if (e.message === "Stop Iteration") return;
}

3. The "Fun" Way: Using every()

every() is a better option. It continues iterating through the collection until the callback function returns false. This effectively acts as a break statement.

comment.comments.every(function (elem) {
    recurs(elem);
    if (...) return false;
    return true;
});

You can also use some() instead of every() if you prefer to return true to break.