Array in JavaScript is undefined

Question

I am very new to JavaScript but have good experience with C and java. For whatever reason my code below will not fill in the array with values other than undefined. I'm trying to simply fill an array with a random set of numbers for a blackjack game

let randomSuite;
let randomNum
let count = 0;
var cards = new Array(56);
window.onload = function main(){
const suites = [
    "H",
    "D",
    "S",
    "C"
];

for(let i = 0 ; i < 56 ; i++){
    randomNum = (Math.random * 12) + 1;
    randomSuite = Math.random * 3;
    cards.push = randomNum;
    console.log(cards[i]);
    count++;
}
alert(cards[1]);
}
function hitFunc(){
    alert("works " + cards[0]);
}

*{
    margin: 0;
    padding : 0;
    font-family: sans-serif;
}

.main{
    width: 100%;
    height: 100vh;
    background-color:black;
}

.img1{
    position: relative;
    z-index: -1;
    margin: 10px auto 20px;
    display: block;
    width: 75%;
    height: 75%;
}

.img2{
    position: relative;
    z-index: 1;
    margin: 10px auto 20px;
    display: block;
    bottom: 200px;
    right: 400px;
    width: 7%;
    height: 7%;
}

.hitButton {
z-index: 1;
position: relative;
text-align: center;
left: 225px;
bottom: 550px;
}

.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
    color: aliceblue;
    object-position: center;
  }

Here's what I have. The alerts are used to show that the function is being completed. Any help is appreciated Please leave an explanation as well. This is my first post on stack overflow let me know if there's anyway to improve the quality of my post.

Rather than cards.push = randomNum; you need cards.push(randomNum);. You are reassigning the push function to a variable here. — Daniel Black
– Daniel Black, Commented May 20, 2022 at 15:39

0stone0 · Accepted Answer · 2022-05-20 15:40:26Z

3

Math.random is a function; use Math.random()
Same for push, use cards.push(randomNum)
You were defining an array with 56 spots new array(56) but since you're using push you'll need to create an empty array so you're pussing to the desired index. Otherwise, instead of push, just set it on the index: cards[i] = randomNum
No need for the count variable since the loop iterator (i) has the same value

let randomSuite;
let randomNum
var cards = new Array();

window.onload = function main(){
    const suites = [
        "H",
        "D",
        "S",
        "C"
    ];

    for(let i = 0 ; i < 56 ; i++){
        randomNum = (Math.random() * 12) + 1;
        randomSuite = Math.random() * 3;
        cards.push(randomNum);
    }
    console.log(cards)
}

*{
    margin: 0;
    padding : 0;
    font-family: sans-serif;
}

.main{
    width: 100%;
    height: 100vh;
    background-color:black;
}

.img1{
    position: relative;
    z-index: -1;
    margin: 10px auto 20px;
    display: block;
    width: 75%;
    height: 75%;
}

.img2{
    position: relative;
    z-index: 1;
    margin: 10px auto 20px;
    display: block;
    bottom: 200px;
    right: 400px;
    width: 7%;
    height: 7%;
}

.hitButton {
z-index: 1;
position: relative;
text-align: center;
left: 225px;
bottom: 550px;
}

.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
    color: aliceblue;
    object-position: center;
  }

answered May 20, 2022 at 15:40

0stone0

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1 Comment

Adam Farrow Over a year ago

Thank you! This worked I stared at this for a little too long.

Mushroomator · Accepted Answer · 2022-05-20 15:46:09Z

Call functions with parenthesis

Math.random() and push() are functions not variables therefore you need to call them using ().

`push()` will append to the array

push() will append a value to the array. You already initialize an array with 10 values. Pushing new values will increase the array size but not add values in the first 10 spots.

const array = new Array(10);

for(let i = 0; i < 10; i++){
  array.push(i);
}
console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Solution

You should instead use array[i] = value; to set a value on a given position.

const array = new Array(10);

for(let i = 0; i < 10; i++){
  array[i] = i;
}
console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

If you want to have a more functional way of doing this as is typical for JavaScript you could use map():

const array = [...new Array(10)].map((_, index) => index);
console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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Array in JavaScript is undefined

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Call functions with parenthesis

`push()` will append to the array

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Call functions with parenthesis

push() will append to the array

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`push()` will append to the array