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javascriptnode.jscallbackinfinite-loopreadline

how to stop infinite loop when using callback inside while-loop in js


so i'm creating a game like Connect 4 which ask an input from a user but the problem i'm facing is that i used callback(readline.question) function inside a while loop whenever i start the code it start infinite loop without asking a question from a user. how i can pause it for a while until user answer? I've to solve this without using async/await.

 function fetchColumn(player, callback) {
   io.question(`Player ${player}, which Column? `, line => {
        console.log(`You requested "${line}"`);
        chosen_column = line;
        callback(); 
    });
}
let connect4 = new Connect4();
connect4.makeBoard(numRows, numCols, winLength);
while (game_over == 0) {
    connect4.printBoard();
    fetchColumn(current_player,()=>{
    
        console.log(`you entered ${chosen_column}`);
        
        if (chosen_column != 'Q' && chosen_column != 'q') {
            move_status = connect4.place_piece(chosen_column, current_player);
            x_in_a_row_status = connect4.x_in_a_row(current_player);
            
            if (move_status == 0) {
// Further code-------

This is what i'm getting in terminal.

Player 1, which Column? 
A B C D E F G 
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . . 
Player 1, which Column? 
A B C D E F G
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .

----------Keep repeating----------

Solution

  • If you want to call an asynchronous function in a loop, you can either use while in combination with await:

    function fetchColumnAsync(player) {
      return new Promise(function(resolve, reject) {
        io.question(`Player ${player}, which Column? `, line => {
          console.log(`You requested "${line}"`);
          chosen_column = line;
          resolve(); 
        });
      });
    }
    let connect4 = new Connect4();
    connect4.makeBoard(numRows, numCols, winLength);
    while (game_over == 0) {
      connect4.printBoard();
      await fetchColumnAsync(current_player);
      console.log(`you entered ${chosen_column}`);
      ...
    }
    

    or recursion in combination with a callback function:

    function loop() {
      if (game_over == 0) {
        connect4.printBoard();
        fetchColumn(current_player, () => {
          console.log(`you entered ${chosen_column}`);
          ...
          loop();
        });
      }
    }
    let connect4 = new Connect4();
    connect4.makeBoard(numRows, numCols, winLength);
    loop();
    

    But you cannot combine while with a callback, because the second iteration of the while loop starts synchronously, before the callback function can be invoked asynchronously. In other words, it gives an infinite loop.