if语句和三元运算符之间的区别

Question

 function findBiggestFraction( a , b ) { a > b ? console.log("a: ", a): ("b: ", b); } var firstFraction = 3/4; var secondFraction = 5/7; findBiggestFraction(firstFraction, secondFraction); // a: 0.75 findBiggestFraction(7/16, 13/25); // b: 0.52 findBiggestFraction(1/2, 3/4); // a: 0.75 function findBiggestFraction( a , b ) { if (a > b) { console.log("a: ", a); } else { console.log("b: ", b); } } var firstFraction = 3/4; var secondFraction = 5/7; findBiggestFraction(firstFraction, secondFraction); // a: 0.75 findBiggestFraction(7/16, 13/25); // b: 0.52 findBiggestFraction(1/2, 3/4); // a: 0.75 

when I run the first code block it only execute the first call. On the other hand for the second block, it runs all three.

Answer 1

您缺少b的console.log 。

a > b ? console.log("a: ", a): console.log("b: ", b);

Answer 2

With the ternary, you're never calling console.log when the condition is false. ("b: ", b) evaluates to b , then you don't do anything with the result.

Roughly equivalent code using an if-statement would be

if (a > b) {
  console.log("a: ", a);
} else {
  ("b: ", b);
}

The mistake is arguably much clearer when you use the more verbose statement. Change the ternary line to

a > b ? console.log("a: ", a) : console.log("b: ", b);

Note that using a ternary to run side effects is generally regarded as bad practice. Either use the ternary inside of console.log to pick what argument to pass in, or use an if-statement.

Answer 3

You're functions are not the same. The first function only prints something if a > b is true. The second function prints either way.

This is a caveat to using the ternary operator. It's very helpful, but can be easy to miss details like you just did.

Summary: Both blocks run both functions, but the first block only prints ~half the time.