条件（三項）演算子 - JavaScript | MDN

Conditional (ternary) operator - JavaScript | MDN Skip to main content Skip to search Conditional (ternary) operator Baseline Widely available This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015. Learn more See full compatibility Report feedback The conditional (ternary) operator is the only JavaScript operator that takes three operands: a condition followed by a question mark ( ? ), then an expression to execute if the condition is truthy followed by a colon ( : ), and finally the expression to execute if the condition is falsy . This operator is frequently used as an alternative to an if...else statement. Try it function getFee(isMember) { return isMember ? "$2.00" : "$10.00"; } console.log(getFee(true)); // Expected output: "$2.00" console.log(getFee(false)); // Expected output: "$10.00" console.log(getFee(null)); // Expected output: "$10.00" Syntax js condition ? exprIfTrue : exprIfFalse Parameters condition An expression whose value is used as a condition. exprIfTrue An expression which is executed if the condition evaluates to a truthy value (one which equals or can be converted to true ). exprIfFalse An expression which is executed if the condition is falsy (that is, has a value which can be converted to false ). Description Besides false , possible falsy expressions are: null , NaN , 0 , the empty string ( "" ), and undefined . If condition is any of these, the result of the conditional expression will be the result of executing the expression exprIfFalse . Examples A basic example js const age = 26; const beverage = age >= 21 ? "Beer" : "Juice"; console.log(beverage); // "Beer" Handling null values One common usage is to handle a value that may be null : js const greeting = (person) => { const name = person ? person.name : "stranger"; return `Howdy, ${name}`; }; console.log(greeting({ name: "Alice" })); // "Howdy, Alice" console.log(greeting(null)); // "Howdy, stranger" Conditional chains The ternary operator is right-associative, which means it can be "chained" in the following way, similar to an if … else if … else if … else chain: js function example() { return condition1 ? value1 : condition2 ? value2 : condition3 ? value3 : value4; } This is equivalent to the following if...else chain. js function example() { if (condition1) { return value1; } else if (condition2) { return value2; } else if (condition3) { return value3; } else { return value4; } } Specifications Specification ECMAScript® 2027 Language Specification # sec-conditional-operator Browser compatibility See also if...else Nullish coalescing operator ( ?? ) Optional chaining ( ?. ) Learn: Making decisions in your code — conditionals Expressions and operators guide Help improve MDN Learn how to contribute This page was last modified on Jul 8, 2025 by MDN contributors . View this page on GitHub • Report a problem with this content