What is the Infinity property used for in Javascript?

问题

Why is the Infinity property used as a command (rather than a result)

For example, this code below works, but the result isn't what I expected.

alert(isOdd(Infinity));

function isOdd(num) { return num%2==1; }

回答1:

MDN REFERENCE

Infinity is a property of the global object, i.e. it is a variable in global scope.

The initial value of Infinity is Number.POSITIVE_INFINITY. The value Infinity (positive infinity) is greater than any other number. This value behaves mathematically like infinity; for example, any positive number multiplied by Infinity is Infinity, and anything divided by Infinity is 0.

First what does this mean? In essence infinity is a concept not an actual value. Mathematics is based on concepts not values. For instance a number isn't a value, a numeral is.

The number 7 is the concept of the intended value, Romans wrote it as VII, in standard form (BASE-10) you write it as 7. In binary(BASE-2) you write it as 111. If you want to use a triangle or any other mark that is fine also as long as the concept is applied correctly.

Now that you know that, Infinity is simply the concept of being greater than any other number. It holds no value. The only reason that the basic concept of an infinity loops means to run forever is because in concept it means that whatever numeral iteration of that loop you are in (whether 1 or a million) infinity will always be greater than that number.

There are many methods to applying concepts in coding which is why everyone's code is ran differently but for example:

SAMPLE TAKEN FROM w3schools:

function findMax(x) {
    var i;
    var max = -Infinity;
    for(i = 0; i < arguments.length; i++) {
        if (arguments[i] > max) {
            max = arguments[i];
        }
    }
    return max;
} 
document.getElementById("demo").innerHTML = findMax(1, 123, 500, 115, 44, 88);

In the site's example they pass the argument of 6 values to the function findMax findMax(1, 123, 500, 115, 44, 88);

They are then using a loop to stop at the parameters length. In the loop they are reassigning the max value from the concept of infinity to a value and if greater than that value when looped again the max value is then changed to the new high value.

Why is this important? Because in the example they use the concept of negative infinity which is simply the values of infinity decremented negatively. One could easily argue that 0 could replace -Infinity but they'd be wrong. This is why.

What if your value range is dependent upon negative values also being passed in the formula above? What if all you have is negative values that were dynamically captured from user input or another function?

Consider findMax was findMax(-1, -10, -15, -20);

0 would give a false output that it was the correct max value which wouldn't be what you wanted. You'd want -1 one to be the output. There are other methods to achieving the solution but for the sake of Infinity concept discussion I will end here.

I hope this sheds more light on the process of Infinity concept.

回答2:

Infinity is a property of the global object that holds a numeric value representing the mathematical concept of infinity. I don't know any normal definition by which it could be called a "command."

With regard to your edit, that should return false (I ran it to confirm this suspicion, and it did on my browser). This is correct, as infinity is not normally considered an odd number.

来源：https://stackoverflow.com/questions/16452076/what-is-the-infinity-property-used-for-in-javascript

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