Left shift (<<) - JavaScript 编辑

The left shift operator (<<) shifts the first operand the specified number of bits to the left. Excess bits shifted off to the left are discarded. Zero bits are shifted in from the right.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

a << b

Description

This operator shifts the first operand the specified number of bits to the left. Excess bits shifted off to the left are discarded. Zero bits are shifted in from the right.

For example, 9 << 2 yields 36:

.    9 (base 10): 00000000000000000000000000001001 (base 2)
                  --------------------------------
9 << 2 (base 10): 00000000000000000000000000100100 (base 2) = 36 (base 10)

Bitwise shifting any number x to the left by y bits yields x * 2 ** y.
So e.g.: 9 << 3 translates to: 9 * (2 ** 3) = 9 * (8) = 72.

Examples

Using left shift

9 << 3; // 72

// 9 * (2 ** 3) = 9 * (8) = 72

Specifications

Specification
ECMAScript (ECMA-262) The definition of 'Bitwise Shift Operators' in that specification.

Browser compatibility

BCD tables only load in the browser

See also

• Bitwise operators in the JS guide
• Left shift assignment operator