what does << do in javascript

Question

Possible Duplicate:
Absolute Beginner's Guide to Bit Shifting?
What is the JavaScript >>> operator and how do you use it?

I came across << while reading some code.

1<<1 //2
2<<1 //4
3<<1 //6
3<<2 //12 

What is this called?

What does this do?

Answer 1

Taken from this answer:

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Left shift (<<)

Integers are stored, in memory, as a series of bits. For example, the number 6 stored as a 32-bit int would be:

00000000 00000000 00000000 00000110

Shifting this bit pattern to the left one position (6 << 1) would result in the number 12:

00000000 00000000 00000000 00001100

As you can see, the digits have shifted to the left by one position, and the last digit on the right is filled with a zero. You might also note that shifting left is equivalent to multiplication by powers of 2. So 6 << 1 is equivalent to 6 * 2, and 6 << 3 is equivalent to 6 * 8. A good optimizing compiler will substitute shifts for multiplications when possible.

Non-circular shifting

Please note that these are not circular shifts. Shifting this value to the left by one position (3,758,096,384 << 1):

11100000 00000000 00000000 00000000

results in 3,221,225,472:

11000000 00000000 00000000 00000000

The digit that gets shifted "off the end" is lost. It does not wrap around.

Answer 2

It's the bitwise left shift operator.

a << b will shift b bits to the left of the binary representation of a.