ECMAScript® 2024 Language Specification

Draft ECMA-262 / February 15, 2024

13.10 Relational Operators

Note 1

The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.

Syntax

RelationalExpression[In, Yield, Await] : ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await] < ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await] > ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await] <= ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await] >= ShiftExpression[?Yield, ?Await] RelationalExpression[?In, ?Yield, ?Await] instanceof ShiftExpression[?Yield, ?Await] [+In] RelationalExpression[+In, ?Yield, ?Await] in ShiftExpression[?Yield, ?Await] [+In] PrivateIdentifier in ShiftExpression[?Yield, ?Await] Note 2

The [In] grammar parameter is needed to avoid confusing the in operator in a relational expression with the in operator in a for statement.

13.10.1 Runtime Semantics: Evaluation

RelationalExpression : RelationalExpression < ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. Let r be ? IsLessThan(lval, rval, true).
  6. If r is undefined, return false. Otherwise, return r.
 RelationalExpression : RelationalExpression > ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. Let r be ? IsLessThan(rval, lval, false).
  6. If r is undefined, return false. Otherwise, return r.
 RelationalExpression : RelationalExpression <= ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. Let r be ? IsLessThan(rval, lval, false).
  6. If r is either true or undefined, return false. Otherwise, return true.
 RelationalExpression : RelationalExpression >= ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. Let r be ? IsLessThan(lval, rval, true).
  6. If r is either true or undefined, return false. Otherwise, return true.
 RelationalExpression : RelationalExpression instanceof ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. Return ? InstanceofOperator(lval, rval).
 RelationalExpression : RelationalExpression in ShiftExpression
  1. Let lref be ? Evaluation of RelationalExpression.
  2. Let lval be ? GetValue(lref).
  3. Let rref be ? Evaluation of ShiftExpression.
  4. Let rval be ? GetValue(rref).
  5. If rval is not an Object, throw a TypeError exception.
  6. Return ? HasProperty(rval, ? ToPropertyKey(lval)).
 RelationalExpression : PrivateIdentifier in ShiftExpression
  1. Let privateIdentifier be the StringValue of PrivateIdentifier.
  2. Let rref be ? Evaluation of ShiftExpression.
  3. Let rval be ? GetValue(rref).
  4. If rval is not an Object, throw a TypeError exception.
  5. Let privateEnv be the running execution context's PrivateEnvironment.
  6. Let privateName be ResolvePrivateIdentifier(privateEnv, privateIdentifier).
  7. If PrivateElementFind(rval, privateName) is not empty, return true.
  8. Return false.

13.10.2 InstanceofOperator ( V, target )

The abstract operation InstanceofOperator takes arguments V (an ECMAScript language value) and target (an ECMAScript language value) and returns either a normal completion containing a Boolean or a throw completion. It implements the generic algorithm for determining if V is an instance of target either by consulting target's @@hasInstance method or, if absent, determining whether the value of target's "prototype" property is present in V's prototype chain. It performs the following steps when called:

  1. If target is not an Object, throw a TypeError exception.
  2. Let instOfHandler be ? GetMethod(target, @@hasInstance).
  3. If instOfHandler is not undefined, then
    1. Return ToBoolean(? Call(instOfHandler, target, « V »)).
  4. If IsCallable(target) is false, throw a TypeError exception.
  5. Return ? OrdinaryHasInstance(target, V).
 Note

Steps 4 and 5 provide compatibility with previous editions of ECMAScript that did not use a @@hasInstance method to define the instanceof operator semantics. If an object does not define or inherit @@hasInstance it uses the default instanceof semantics.