Return返回Javascript中未定义的返回

Question

I need to write a program to traverse a maze in Javascript where 1 is the source and 2 is the destination and 3 is a path and 0 is a wall. Below is the code which I have written. The code is correct but I get the answer only when I use console.log() and not when I return the strings yes or no. Why does it happen so?

function sourceDes(arr) {
for (var i=0;i<arr.length;i++) {
    for (var j=0;j<arr[i].length; j++) {
        if (arr[i][j] == 1) {
            traverse(i,j);
            break;
        }
    }
}

function traverse(rowPos, colPos) {
            if (arr[rowPos][colPos] == 2) {
                console.log("yes");
                // return "Yes";
            }
            else if (arr[rowPos][colPos] == 3 || arr[rowPos][colPos] == 1) {
                arr[rowPos][colPos] = 9;

                if(rowPos < arr.length - 1) {
                    return traverse(rowPos + 1, colPos);
                }
                if(colPos < arr[rowPos].length - 1) {
                    return traverse(rowPos, colPos + 1);
                }
                if(rowPos > 0) {
                    return traverse(rowPos - 1, colPos);
                }
                if(colPos > 0) {
                    return traverse(rowPos, colPos - 1);
                }
            }               
            else if (arr[rowPos][colPos] == 0) {
                console.log("No");
                // return "No";
            }
        }
}

input

arr = [[3, 0, 0, 0], [0, 3, 3, 0], [0, 1, 0, 3], [0, 2, 3, 3]];
answer = sourceDes(arr);
answer;

output when console.log()

yes

output when value is returned and console.log is applied on function

undefined

Answer 1

您在sourceDes函数中缺少return语句

Answer 2

return语句应同时在两个函数中，否则返回undefined

Answer 3

In Javascript when you omit a return statement inside a function then an implicit return undefined is assumed. That's why you get this returned value.

Answer 4

I have checked your code and found a bug in your sourceDes function. You do not define the return statement in the function.

function sourceDes(arr) {
for (var i=0;i<arr.length;i++) {
    for (var j=0;j<arr[i].length; j++) {
        if (arr[i][j] == 1) {
            traverse(i,j);
            break;
        }
    }
}

When the loop run for last time, your if condition is getting false that is why it iss returing undefined . Check code below I Have added the else part and it return No when your if condition is false.

 arr = [[3, 0, 0, 0], [0, 3, 3, 0], [0, 1, 0, 3], [0, 2, 3, 3]]; function sourceDes(arr) { for (var i=0;i<arr.length;i++) { for (var j=0;j<arr[i].length; j++) { if (arr[i][j] == 1) { traverse(i,j); break; } else{ return "No"; } } } function traverse(rowPos, colPos) { if (arr[rowPos][colPos] == 2) { console.log("yes"); return "Yes"; } else if (arr[rowPos][colPos] == 3 || arr[rowPos][colPos] == 1) { arr[rowPos][colPos] = 9; if(rowPos < arr.length - 1) { return traverse(rowPos + 1, colPos); } if(colPos < arr[rowPos].length - 1) { return traverse(rowPos, colPos + 1); } if(rowPos > 0) { return traverse(rowPos - 1, colPos); } if(colPos > 0) { return traverse(rowPos, colPos - 1); } } else if (arr[rowPos][colPos] == 0) { console.log("No"); return "No"; } } } answer = sourceDes(arr); document.write(answer); 

Answer 5

Use following code snippet. I have added variable and set the value in it in loop and returned the result variable at the end of function.

function sourceDes(arr) {
var result='';
for (var i=0;i<arr.length;i++) {
    for (var j=0;j<arr[i].length; j++) {
        if (arr[i][j] == 1) {
           result= traverse(i,j);
            break;
        }
    }
 return result;
}

function traverse(rowPos, colPos) {
            if (arr[rowPos][colPos] == 2) {
                //console.log("yes");
                 return "Yes";
            }
            else if (arr[rowPos][colPos] == 3 || arr[rowPos][colPos] == 1) {
                arr[rowPos][colPos] = 9;

                if(rowPos < arr.length - 1) {
                    return traverse(rowPos + 1, colPos);
                }
                if(colPos < arr[rowPos].length - 1) {
                    return traverse(rowPos, colPos + 1);
                }
                if(rowPos > 0) {
                    return traverse(rowPos - 1, colPos);
                }
                if(colPos > 0) {
                    return traverse(rowPos, colPos - 1);
                }
            }               
            else if (arr[rowPos][colPos] == 0) {
                //console.log("No");
                 return "No";
            }
        }
}