如果声明出于某种原因表现得很奇怪

Question

So I have an if statement that is checking the values of a drop down. The user has to select at least one of them to continue. The values are just numbers. My if statement checks to see that, basically, the values are equal to zero:

if (numChildren === 0 && numAdults === 0){
    Than do this
}

But for some reason it keep returning false. I have console logged the numChildren and adults to see what there values are and they are zero I have no idea why it isn't working I have put a "!" before it to cause it to be true but then it remains false. It is a very weird error.

$("#Discounts").on("click", function () {
        let numChildren = $("#children").val();
        let numAdults = $("#adults").val();
        console.log("Adults: " + numAdults + "\nChildren: " + numChildren);
        console.log(numChildren === 0 && numAdults === 0);
        if (numChildren === 0 && numAdults === 0) {
            alert("You must select");
            $("#children").val(1);
        }
    });

Answer 1

It's not weird.

You are using the triple equal comparison and, probably, the numChildren contains a number in string form (like "0") which you are comparing to zero as an actual number.

It should work with:

numChildren == 0 && numAdults == 0

or

Number(numChildren) === 0 && Number(numAdults) === 0

This is the official reference: https://tc39.github.io/ecma262/#sec-strict-equality-comparison

Answer 2

When you use 3 equals in a if statement the numChildren must be the same type and value as 0 (integer), not just equal to 0.

Try changing to 2 equals:

if (numChildren == 0 && numAdults == 0) {
            alert("You must select");
            $("#children").val(1);
        }

Reference

Answer 3

You can try this:

if (Number(numChildren) === 0 && Number(numAdults) === 0) {
        alert("You must select");
        $("#children").val(1);
}