Null>=0 And Undefined>=0 Have Opposite Result Values
Recently, I unified the use of null and undefined in the project according to a technical specification of the company. The variables in some scenarios, whose initial values were undefined, are now changed to null. After the modification, I found a strange bug that I couldn't find no matter how hard I tried. The logic of the code from top to bottom was normal, but at the end it threw an exception that shouldn't have been thrown. So I cloned the code again and restored it to the state before the modification. Then I ran the code before and after the modification at the same time. I found that when the code came to an if branch, one of them entered the if branch and the other jumped over it. The if branch looked like this: const count = pageKidsCountCache.get(currentNode); // Skip nodes where the page can't be. if (count >= 0 && currentPageIndex + count =0 was false. But after changing it to null, it became true. This caused a strange problem. I entered it twice in the Chrome console and found that JavaScript is indeed like this. The result value of null>=0 is true, while the result value of undefined>=0 is false. To further alleviate my confusion, I consulted some documents. The data shows that: When using relational operators, JavaScript converts non-numeric operands to numbers. By default, null is converted to 0, and undefined is converted to NaN. Because 0>=0, null>=0 is true, and NaN is false when compared to any number, so the value of undefined>=0 is false.
Recently, I unified the use of null and undefined in the project according to a technical specification of the company. The variables in some scenarios, whose initial values were undefined, are now changed to null.
After the modification, I found a strange bug that I couldn't find no matter how hard I tried. The logic of the code from top to bottom was normal, but at the end it threw an exception that shouldn't have been thrown.
So I cloned the code again and restored it to the state before the modification. Then I ran the code before and after the modification at the same time. I found that when the code came to an if branch, one of them entered the if branch and the other jumped over it. The if branch looked like this:
const count = pageKidsCountCache.get(currentNode);
// Skip nodes where the page can't be.
if (count >= 0 && currentPageIndex + count <= pageIndex) {
currentPageIndex += count;
continue;
}
The value count retrieved from the Map is sometimes empty, that is, undefined. In this case, I changed it to null. Then something went wrong. When the count value was undefined, count>=0 was false. But after changing it to null, it became true. This caused a strange problem.
I entered it twice in the Chrome console and found that JavaScript is indeed like this.
The result value of null>=0 is true, while the result value of undefined>=0 is false.
To further alleviate my confusion, I consulted some documents. The data shows that:
When using relational operators, JavaScript converts non-numeric operands to numbers. By default, null is converted to 0, and undefined is converted to NaN. Because 0>=0, null>=0 is true, and NaN is false when compared to any number, so the value of undefined>=0 is false.
