Get the value of the drop-down list box as an array, split, $.inArray example_javascript skills

I encountered a broken problem today:

1. I clicked the event from a drop-down list select to get the value of options

Copy Code The code is as follows:

var product_id = $(this).val()

When the console.log comes out, it is found to be an array. , such as: ["51"]

Then make the following judgment

Copy the code The code is as follows:

console.log(product_id);
if(product_id == '51'){alert(111);}
if(product_id[0] == '51'){alert (222);}

I found that a prompt box can pop up, isn’t this a trick on me?

2. I use this product_id to match whether it is included in an array

Error code:

Copy code The code is as follows:

var result = $. inArray(product_id,arr_product_ids);

Correct code:

Copy code The code is as follows:

var result = $.inArray(product_id[0],arr_product_ids);

$.inArray() must use product_id[0], which means that arrays cannot be used

I didn’t know until today that the value obtained by the drop-down list is an array. If someone knows more about it, please explain.