除了用于!!
强制布尔值之外,您还可以使用switch
语句来评估真/假:
switch (true) { // use a boolean to force case statement to evaluate conditionals
case (val ? true : false): // force a truthy/falsy evaluation of val using parentheses and the ternary operator
console.log(val + ' evaluates as truthy in the switch statement.');
break;
default:
console.log(val + ' evaluates as falsy in the switch statement.');
break;
}
这是一组函数和测试,您可以自己查看:
(function () {
'use strict';
var truthitizeSwitch = function (val) {
switch (true) { // use a boolean to force case statement to evaluate conditionals
case (val ? true : false): // force a truthy/falsy evaluation of val using parentheses and the ternary operator
console.log(val + ' evaluates as truthy in the switch statement.');
break;
default:
console.log(val + ' evaluates as falsy in the switch statement.');
break;
}
return !!val; // use !! to return a coerced boolean
},
truthitizeIf = function (val) {
if (val) { // if statement naturally forces a truthy/falsy evaluation
console.log(val + ' evaluates as truthy in the if statement.');
} else {
console.log(val + ' evaluates as falsy in the if statement.');
}
return !!val; // use !! to return a coerced boolean
},
tests = [
undefined, // falsey: undefined
null, // falsey: null
parseInt('NaNificate this string'), // falsey: NaN
'', // falsey: empty string
0, // falsey: zero
false, // falsey: boolean false
{}, // truthy: empty object
{"foo": "bar"}, // truthy: non-empty object
-1, // truthy: negative non-zero number
'asdf', // truthy: non-empty string
1, // truthy: positive non-zero number
true // truthy: boolean true
],
i;
for (i = 0; i < tests.length; i += 1) {
truthitizeSwitch(tests[i]);
truthitizeIf(tests[i]);
}
}());
而且,当然:),强制性的jsFiddle:http: //jsfiddle.net/AE8MU/