The logical OR (|| ) operator (logical disjunction) for a set of operands is true if and only if one or more of its operands is true. It is typically used with boolean (logical) values. When it is, it returns a Boolean value. However, the || operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value. Description If expr1 can be converted to true , returns expr1 ; else, returns expr2 . If a value can be converted to true , the value is so-called truthy. If a value can be converted to false , the value is so-called
falsy. Examples of expressions that can be converted to false are: null ;NaN ;0 ;- empty string (
"" or '' or `` ); undefined .
Even though the || operator can be used with operands that are not Boolean values, it can still be considered a boolean operator since its return value can always be converted to a
boolean primitive. To explicitly convert its return value (or any expression in general) to the corresponding boolean value, use a double NOT operator or the
Boolean constructor. Short-circuit evaluation The logical OR
expression is evaluated left to right, it is tested for possible "short-circuit" evaluation using the following rule:
(some truthy expression) || expr is short-circuit evaluated to the truthy expression. Short circuit means that the expr part above is not evaluated, hence any side effects of doing so do not take effect (e.g., if expr is a function call, the calling never takes place). This happens because the value of the operator is already determined after the evaluation of
the first operand. See example: function A(){ console.log('called A'); return false; }
function B(){ console.log('called B'); return true; }
console.log(B() || A());
// logs "called B" due to the function call,
// then logs true (which is the resulting value of the operator)
Operator precedence The following expressions might seem equivalent, but they are not, because the && operator is executed before the || operator (see
operator precedence). true || false && false // returns true, because && is executed first
(true || false) && false // returns false, because grouping has the highest precedence
Using ORThe following code shows examples of the || (logical OR) operator. o1 = true || true // t || t returns true
o2 = false || true // f || t returns true
o3 = true || false // t || f returns true
o4 = false || (3 === 4) // f || f returns false
o5 = 'Cat' || 'Dog' // t || t returns "Cat"
o6 = false || 'Cat' // f || t returns "Cat"
o7 = 'Cat' || false // t || f returns "Cat"
o8 = '' || false // f || f returns false
o9 = false || '' // f || f returns ""
o10 = false || varObject // f || object returns varObject
Note: If you use this operator to provide a default value to some variable, be aware that any falsy value will not be used. If you only need to filter out
null or undefined , consider using the nullish coalescing operator. Conversion rules for booleansConverting AND to ORThe following operation involving booleans: bCondition1 && bCondition2
is always equal to: !(!bCondition1 || !bCondition2)
Converting OR to ANDThe following operation involving booleans: bCondition1 || bCondition2
is always equal to: !(!bCondition1 && !bCondition2)
Removing
nested parentheses As logical expressions are evaluated left to right, it is always possible to remove parentheses from a complex expression following some rules. The following composite operation involving booleans: bCondition1 && (bCondition2 || bCondition3)
is always equal to: !(!bCondition1 || !bCondition2 && !bCondition3)
Specifications
Specification |
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ECMAScript Language Specification # prod-LogicalORExpression
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What are the 5 logical operators?
There are five logical operator symbols: tilde, dot, wedge, horseshoe, and triple bar.
Is == a logical operator?
The operators include: > , < , >= , <= , === , and !== . Logical operators — operators that combine multiple boolean expressions or values and provide a single boolean output.
Which of the following is logical operator Mcq?
|| is a Logical OR operator.
What are the four logical operators?
Logical Operators are used to perform logical operations and include AND, OR, or NOT. Boolean Operators include AND, OR, XOR, or NOT and can have one of two values, true or false.
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