What does i << 1 mean in Javascript?

Question

I was going through some code for prime numbers on Stack and found this.

I tried experimenting with this for sometime and figured this :

var i = 5;
var j = 0;

If i write j = i << 1, all it does is assigns (i * 2) ie - 10 in this case to j

If i write j = i << 2, (i * 2) * 2 ie - 10 * 2 .....and so on.

Now i have a doubt what actually this operator does ?

I tried googling this, but did not find any straight solution to this.

@SubirKumarSao — Java and JavaScript are not the same thing (like Car and Carpet are not the same thing). — Quentin, Jun 05 '13 at 12:46
please do your research (google) before hitting stackoverflow. — kumarharsh, Jun 05 '13 at 12:47
@Quentin : They are exactly the same things as far as this operator is concerned. — kumarharsh, Jun 05 '13 at 12:48
@Harsh — But pointing to documentation for a different programming language without explaining that they work in the same way is a good way to confuse people. — Quentin, Jun 05 '13 at 12:52
yeah, point taken. although Car and Carpet??? i don... Oh... now i get it!!! NICE :) — kumarharsh, Jun 05 '13 at 12:53

score 6 · Accepted Answer · answered Jun 05 '13 at 12:44

6

Those are Bitwise Operators in Javascript.

Bitwise operators treat their operands as a sequence of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.

Left Shift Operator :

a << b : Shifts a in binary representation b (< 32) bits to the left, shifting in zeros from the right.

answered Jun 05 '13 at 12:44

AllTooSir

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I want to add, they do the same thing in PHP. – David Bélanger Jun 05 '13 at 12:44
It's also worth noting that the left operand is converted an int32, and the right operand is converted to a uint32 before the operation is performed, per the [spec](http://es5.github.io/#x11.7.1). – Peter Olson Jun 05 '13 at 12:51

score 1 · Answer 2 · answered Jun 05 '13 at 12:44

1

<< is the left shift operator. Each bit would shift left the number of times specified. Example: n<<2 would bitwise shift n 2 times, adding zeros to the right.

n=4  // 0000 0000 0000 0100
n<<2 //<= 0000 0000 0001 0000 - Value is 16

answered Jun 05 '13 at 12:44

karthikr

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score 0 · Answer 3 · answered Jun 05 '13 at 12:45

The << operator^{[ES5 spec]} is the left bit shift operator. It takes the number on the left and shifts the bits as many places as the number on the right. i << 2, for example, will shift the digits of i to the left 2 places.

var i = 5;  // i: 0000 0000 0000 0101
i = i << 2; // i: 0000 0000 0001 0100

What does i << 1 mean in Javascript?

3 Answers3