Pls i dont understand the code

function multiplyAll(arr) {
var product = 1;
// Only change code below this line,
for(var i = 0; i < arr.length; i++){
for(var j = 0; j < arr[i].length; j++){
product = product *= arr[i][j];
}
}
// Only change code above this line return product; }

// Modify values below to test your code
multiplyAll([[1,2],[3,4],[5,6,7]]);

Can someone explain the code to me?

what is it that you don’t understand?
if you explain what you understand it is easier to help you

without knowing anything I can suggest you look at your code using this tool: http://pythontutor.com/javascript.html#mode=edit

We have a function that is a piece of code with name multiplyAll and one parameter arr.
We are initializing var product to 1.
for loop normally has three arguments:
we are iterating from index 0 till index of arr.length adding 1:
index: 0, 1, 2, …, arr.length-1
We have multidimensional array:
if we look at example below
index0 contains array [1,2],
index1 contains array [3,4]
index arr.legth-1 contains array [5, 6, 7]
so we need a second for loop to iterate inside of that child arrays:
form index 0 till index arr[i].lenght:
if we look at example below
arr[0] is [1,2]
we are moving forwards so:
for arr[0] => [1,2], for arr[0][0] => 1
product * 1
product is initialized to 1, it means
1 * 1
product = 1
We are going back because we can go 1 step forward till we will find arr.length
product = 1
i = 0, because we have not reached arr[i].length-1
j = 1, because we are passed calculation with j= 0
for arr[0][1] =>2, product 1
product = 1 * 2
product = 2
i = 1, j = 0, product = 2 and so we are going…
After this all process our function returns a product.

Did you take a look at the explanation given in the Guide? What part of that explanation do you not understand?

It is one mistake in code example:
// Only change code above this line return product; }
Change so:

// Only change code above this line 
return product;
}