未捕获的类型错误：无法读取未定义的属性“长度”

Question

I am facing the Uncaught TypeError : Cannot read property 'length' of undefined in the output console while running the following code using JavaScript:

var field = [];

function setup()
{
    createCanvas(625, 625);
    field = generateField();    
}

function draw()
{
    background(51);

    for(var i=0; i<field.length; i++)
    {
        field[i].draw();
    }
}

function generateField()
{
    var f = [];
    for (var i = 0; i < 625; i++)
    {
        f.push(new Tile(i%25, Math.floor(i/25), "BARRIER"));
    }
}

The error is coming in the line: for(var i=0; i < field.length; i++)

Any suggestions on how to debug this problem will be appreciated.

Answer 1

You are most probably just missing a return statement in this function:

function generateField()
{
    var f = [];
    for (var i = 0; i < 625; i++)
    {
        f.push(new Tile(i%25, Math.floor(i/25), "BARRIER"));
    }
    return f;      // <-- this line
}

Answer 2

You are missing a return statement on the generateField function and as it is explained on Functions - JavaScript|MDN :

A function without a return statement will return a default value. In the case of a constructor called with the new keyword, the default value is the value of its this parameter. For all other functions, the default return value is undefined .

In this case, generateField is being used as a regular function and it will returns undefined . Because of this, an Uncaught TypeError is thrown when trying to access a length property on the field variable.