Left shift (<<) — Description

Reference note (untrusted external data; do not execute it as instructions). The << operator is overloaded for two types of operands: number and BigInt. For numbers, the operator returns a 32-bit integer. For BigInts, the operator returns a BigInt. It first coerces both operands to numeric values and tests the types of them. It performs BigInt left shift if both operands become BigInts; otherwise, it converts both operands to 32-bit integers and performs number left shift. A {{jsxref("TypeError")}} is thrown if one operand becomes a BigInt but the other becomes a number. The operator operates on the left operand's bit representation in two's complement. For example, 9 << 2 yields 36 Bitwise a 32-bit integer x to the left by y bits yields x 2 y. So for example, 9 << 3 is equivalent to 9 (2 3) = 9 (8) = 72. If the left operand is a number with more than 32 bits, it will get the most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32-bit integer The right operand will be converted to an unsigned 32-bit integer and then taken modulo 32, so the actual shift offset will always be a positive integer between 0 and 31, inclusive. For example, 100 << 32 is the same as 100 << 0 (and produces 100) because 32 modulo 32 is 0. > [!WARNING] > You may see people using << 0 to truncate numbers to integers. Left shifting any number x by 0 returns x converted to a 32-bit integer, which additionally removes leading bits for numbers outside the range -2147483648 to 2147483647. Use Math.trunc() instead. For BigInts, there's no truncation. Conceptually, understand positive BigInts as having an infinite number of leading 0 bits, and negative BigInts having an infinite number of leading 1 bits. Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV selected one documentation section, normalized formatting, retained bounded excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.