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4.13.1 The Conditional Operator (?:)

4.13.1 The Conditional Operator (?:)


The conditional operator is the only ternary operator (three operands) in JavaScript and is sometimes actually called the ternary operator. This operator is sometimes written ?:, although it does not appear quite that way in code. Because this operator has three operands, the first goes before the ?, the second goes between the ? and the :, and the third goes after the :. It is used like this:

x > 0 ? x : -x // The absolute value of x

The operands of the conditional operator may be of any type. The first operand is evaluated and interpreted as a boolean. If the value of the first operand is truthy, then the second operand is evaluated, and its value is returned. Otherwise, if the first operand is falsy, then the third operand is evaluated and its value is returned. Only one of the second and third operands is evaluated, never both.

While you can achieve similar results using the if statement ( §5.4.1 ), the ?: operator often provides a handy shortcut. Here is a typical usage, which checks to be sure that a variable is defined (and has a meaningful, truthy value) and uses it if so or provides a default value if not:

greeting = "hello " + (username ? username : "there");

This is equivalent to, but more compact than, the following if statement:

greeting = "hello "; if (username)

greeting += username; else

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