--- title: Less than (<) slug: Web/JavaScript/Reference/Operators/Less_than translation_of: Web/JavaScript/Reference/Operators/Less_than ---

The less than operator (<) returns true if the left operand is less than the right operand, and false otherwise.

{{EmbedInteractiveExample("pages/js/expressions-less-than.html")}}

语法

 x < y

Description

The operands are compared using the Abstract Relational Comparison algorithm, which is roughly summarised below:

First, objects are converted to primitives using Symbol.ToPrimitive with the hint parameter be 'number'.
If both values are strings, they are compared as strings, based on the values of the Unicode code points they contain.
Otherwise JavaScript attempts to convert non-numeric types to numeric values:
- Boolean values true and false are converted to 1 and 0 respectively.
- null is converted to 0.
- undefined is converted to NaN.
- Strings are converted based on the values they contain, and are converted as NaN if they do not contain numeric values.
If either value is NaN, the operator returns false.
Otherwise the values are compared as numeric values.

Examples

String to string comparison

console.log("a" < "b");        // true
console.log("a" < "a");        // false
console.log("a" < "3");        // false

String to number comparison

console.log("5" < 3);          // false
console.log("3" < 3);          // false
console.log("3" < 5);          // true

console.log("hello" < 5);      // false
console.log(5 < "hello");      // false

console.log("5" < 3n);         // false
console.log("3" < 5n);         // true

Number to Number comparison

console.log(5 < 3);            // false
console.log(3 < 3);            // false
console.log(3 < 5);            // true

Number to BigInt comparison

console.log(5n < 3);           // false
console.log(3 < 5n);           // true

Comparing Boolean, null, undefined, NaN

console.log(true < false);     // false
console.log(false < true);     // true

console.log(0 < true);         // true
console.log(true < 1);         // false

console.log(null < 0);         // false
console.log(null < 1);         // true

console.log(undefined < 3);    // false
console.log(3 < undefined);    // false

console.log(3 < NaN);          // false
console.log(NaN < 3);          // false

Specifications

Specification
{{SpecName('ESDraft', '#sec-relational-operators', 'Relational operators')}}

语法