Less than (<)

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

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
ECMAScript (ECMA-262)
Relational operators

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Less than (a < b)Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 3Opera Full support 3Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support 0.1.100

Legend

Full support  
Full support

See also