在JavaScript中使用Double Equals是否会导致性能问题？

Question

Per "strict mode" in JavaScript, you should use === when comparing values in an if-statement. However, when dealing with truthy/falsy values, this can lead to very long if-statements:

if (a !== null && a !== undefined && a !== '' && a !== 0) {}

To get around this, I've started using !!

if(!!a === true) {}

to cast the value as a boolean. However, I'm concerned there's a performance impact. According to my JSPerf ( http://jsperf.com/double-exclamation-vs-falsy/4 ), This approach is 30% slower than the long form of the if-statement.

Am I way off base here? Has anyone else noticed a performance hit?

Answer 1

Using if(!!a) { does have a significant performance hit because you're doing the same boolean conversion that JS does internally when you do if(a) . It is more performant to do explicit type checking like if(a === true) or if(a !== null && a !== undefined)