JavaScript bitwise NOT ~ doesn't produce same result

Question

I am attempting to invert the binary digits of a base-10 value using JavaScript, according to this W3Schools page, JavaScript's Bitwise NOT operator (i.e. ~) should do just that.

In an example they show ~5 resulting in a value of 10, but when I attempt to execute the simple program ...

console.log(~5);

... the RTE logs -6, not 10. What am I doing wrong?

The example you are referring to uses 4-bit unsigned numbers. In the real world using 32-bit or 64-bit *signed* numbers, `~5` is `-6`, as you can see from the other examples on the same page. However, since the page doesn't mention it is working with 4-bit unsigned numbers it is misleading. Try to find a better tutorial, there are plenty of questions on [so] that prove that w3schools is a source of low-quality information. — axiac, Nov 27 '17 at 20:30
I love that there's even a big yellow box that says, "Because of this ~ 5 returns 10." — Mark, Nov 27 '17 at 20:32

score 2 · Accepted Answer · answered Nov 27 '17 at 20:53

If you scroll down a bit at the website (https://www.w3schools.com), you find this information (as axiac has already written):

The examples above uses 4 bits unsigned binary numbers. Because of this ~ 5 returns 10.

Since JavaScript uses 32 bits signed integers, it will not return 10. It will return -6.

00000000000000000000000000000101 (5)

11111111111111111111111111111010 (~5 = -6)

A signed integer uses the leftmost bit as the minus sign.

So you didn’t do anything wrong.

var x = 5;
document.getElementById("output").innerHTML=~5;

<div id="output"></div>

JavaScript bitwise NOT ~ doesn't produce same result

1 Answers1