# JavaScript - left shift operator assignment

The Bitwise left shift assignment operator (<<=) assigns the first operand a value equal to the result of Bitwise left shift operation of two operands.

(x <<= y) is equivalent to (x = x << y)

The Bitwise left shift operator (<<) takes the two numbers and left shift the bits of first operand by number of place specified by second operand. For example: for left shifting the bits of x by y places, the expression (x<<y) can be used. It is equivalent to multiplying x by 2y.

The example below describes how left shift operator works:

```1000 << 2 returns 4000

(In Binary)
1000         ->    1111101000
<< 2                     |  left shift the bits
-----                    V  by 2 places
4000         <-  111110100000
(In Binary)
```

The code of using left shift operator (<<) is given below:

```var x = 1000;
var txt;

//left shift assignment operation
x <<= 2;
txt = "x = " + x;
```

The output (value of txt) after running above script will be:

```x = 4000
```

### Example: Count number of 1 Bits in a positive integer

Consider an integer 1000. In the bit-wise format, it can be written as 1111101000. However, all bits are not written here. A complete representation will be 32 bit representation as given below:

```00000000000000000000001111101000
```

Bitwise AND operation with 1 at any bit results into 1 if the bit is 1 or 0 if the bit is 0. Performing such operation at every bit, and counting the number of 1 gives the count of 1 bits in the given positive integer. To achieve this bitwise left shift assignment operator can be used as shown in the example below:

```function CountOneBits(n) {
var count = 0;

//performing bitwise AND operation
//at every bit of the number
for(i = 0; i < 32; ++i) {
count++;
}
return count;
}

var txt;
txt = "CountOneBits(1000) = " +
CountOneBits(1000) + "<br>";
txt = txt + "CountOneBits(1023) = "+
CountOneBits(1023) + "<br>";
```

The output (value of txt) after running above script will be:

```CountOneBits(1000) = 6
CountOneBits(1023) = 10
```

❮ JavaScript - Operators

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